Storing new marine batteries

[lkruper]

SunEagle pretty well answered that from a cost perspective. AGM cost roughly twice as much and last half as long as making them some 400% more expensive then FLA from cradle to grave. Same as Lithium, in the end much higher cost than FLA.

To expand a bit AGM does have niche applications neither FLA or Lithium can match. Depends on application.

One you named much lower Self Discharge Rates. When fully charged up and stored in cool temps about the same as Lithium at 1% per month. Charge an AGM up to 100%, store it at 30's F temps and you can easily store them a year.

High Charge Rates and Discharge Rates. Lithium can do that but not Deep Cycle FLA. When you hear the kooks with a 12 volt 100 AH battery with a 1000 watt Inverter, it had better be a high quality expensive AGM battery. Otherwise load that Inverter up more than 200 watts, and your Inverter is going to trip off-line from under voltage despite the battery is fully charged up. Live in an area with less than 3 Sun Hours in winter, you need AGM because you are looking at Charge rates exceeding C/6 unless you have 8 or more days reserve capacity.

Low Charge Rate of less than C/12. FLA needs at least C/12 to prevent stratification and to dissolve soft lead sulfate crystals from normal discharge depths.

Extreme cold environments.

Mobile applications or other Installations where spills and gassing are unacceptable like an Air Plane, Space Craft, Inverted or Side Mounted.

Where Deep Discharges are encountered frequently and/or routinely.

So AGM's and Lithium have their place, but cost needs to be justified when you are talking as much as 400% higher cost over FLA.

Is it true that LiFePO batteries permanently lose capacity just sitting (cycles as well as chronological life) at a rate higher than lead acid?

[SunEagle]

Is it true that LiFePO batteries permanently lose capacity just sitting (cycles as well as chronological life) at a rate higher than lead acid?

I am not sure about LiFePO batteries but someone is doing the math on Lithium ion battery aging.

[Sunking]

Is it true that LiFePO batteries permanently lose capacity just sitting (cycles as well as chronological life) at a rate higher than lead acid?

The answer can be YES or NO. Again it is being Stuck inside the Lead Acid Battery Box mentality.

When you are stuck inside the lead acid battery box all you know is: YOU MUST CHARGE TO 100% SOC OR BAD THINGS HAPPEN. That is true for Lead Acid batteries and most other chemistry as anything less than 100% SOC accelerates aging and capacity loss.

So with the Mind Set of Lead Acid batteries will destroy your Lithium Battery. Anytime you charger a Lithium Battery to 100% does damage and accelerates the aging process which results in capacity loss and cycle life. Leave or store Lithium batteries at 100% is a guaranteed recipe for a very short battery life. Read any spec of a lithium battery and they list Cycle Life vs SOC. Goes something like this: 500 cycles @ 100% SOC to 10% DOD. 1000 cycles @ 80 or 90% SOC to 20% DOD. That should answer your question.

So YES charging your lithium battery to 100% will shorten the life. If you want to kill it faster, store it at 100% SOC is a recipe for dead battery. When you store a lithium battery you do so in the range of 40 to 60% SOC. Chest beating manufactures say must be stored at 60 to 70% which is a half truth and half BS. They ship at 70% which yields the longest possible shelf life. 20 to 40% is just as safe and less less stress on them, you just do not get maximum storage time. Think of Lithium as a Balloon.

Takeaway for maximum cycle and calendar life charge to 80% max, and do not go below 20%. Never exceed 90% or go below 10% for decent cycle and calendar life. Or you can be a consumer, use top balance to 100% which makes manufactures very happy because you will be back soon to replace them. Regardless if you only charge to 80,90, or 100% if you go to or flirt with 100% DOD aka 0% SOC game over. If you Top Balance and use Balance Boards, you have set up the perfect storm conditions to destroy your batteries. Manufactures love that.

[MikeCanuck]

PNjunction
re: please resist the temptation to run down to Canadian Tire and pick up the cheapest little trickler around.
re: May I suggest the best of both worlds - the Tecmate-Optimate 6 charger. The float here is a 50% duty cycle of 30 mins on / 30 mins off. That actually helps put a *little* activity into your bank, rather than sitting at a steady-state, or no state much of the time like most others. Aside from that, your battery is tested every 12 hours. Plus, there is nothing to set, but plug in and walk away. If you want to know what all the blinkenlights mean, you can get into that too, but not totally necessary.

Arg, I already have a Canadian Tire smart charger that I use on my other junky batteries
It's not a cheapy trickle charger, it charges from from 0-12A and actually seemed to have revived a partly sulphated cell on one junky battery ("desulphation/recondition mode") after I topped it back off with water and kept cycling the charger for a week until no errors and 100% charged. So I kinda like it.
But when on float ("maintenance mode"), I suspect it acts the way you're saying cheapy smart chargers work, since it is always shows 0.0A charging on float. That Tecmate-Optimate 6 is very tempting but it's $145 up here. I'll put it on my wish list to mrs. santa then put on the earplugs
So based on everyone's advice here, I think I'll take mr. poor man's approach for time being; do things well best I can but do it manually.
Every few weeks, I'll give the batteries some exercise etc, then put it back up on float. Or when lazy, I might of read somewhere here of someone putting their smart charger on a timer so every day it kicks the battery for a alittle while, but that may be too much...
I don't mind manual though, I see this stuff as fun hobby learning with all the great experienced advice from you guys, and I'm keeping my costs low while having fun while having practical uses for the hobby


lkruper re: I wonder about what your cost would be to get two 6v golf cart batteries to make a 12v serial bank instead of two 12v marine batteries in parallel. Where I live, the Marine battery at Costco is more expensive per AH than their golf cart batteries.
There are also arguably advantages to charging two batteries in series compared to two in parallel.

I get green with envy every time I see a post about golf cart batteries and how much more value they are than marine, esp from costco. Golf cart batteries are expensive here Trojan T105RE is at least cad$200 plus shipping, taxes and death with no beer money left after buying 2 of those. Costco's don't carry golf cart battteries up here, I've called every costco within 100 mile radius. Costco's here have actually dropped carrying even marine batteries altogether and only sell auto batteries since early this year when I was looking for them for my other (solar) setup for my shed. I guess not enough demand here in the great white north, not enough boaters, RVers and golfers during above 0C (30F) t-shirt and shorts season. Walmart doesn't carry golf carts either and now is the only place I can get cheap decent warranty marine batteries.

[Sunking]

I get green with envy every time I see a post about golf cart batteries and how much more value they are than marine, esp from costco. Golf cart batteries are expensive here Trojan T105RE is at least cad$200 plus shipping, taxes and death with no beer money left after buying 2 of those. Costco's don't carry golf cart battteries up here, I've called every costco within 100 mile radius. Costco's here have actually dropped carrying even marine batteries altogether and only sell auto batteries since early this year when I was looking for them for my other (solar) setup for my shed. I guess not enough demand here in the great white north, not enough boaters, RVers and golfers during above 0C (30F) t-shirt and shorts season. Walmart doesn't carry golf carts either and now is the only place I can get cheap decent warranty marine batteries.

I got to poke some fun at Canucks. You already answered why you cannot find good batteries up there. You spend all your money and time drinking beer while fishing and hunting in winter. Only damn batteries you need is to start your snowmobiles to make a Beer Run from deer camp or the ice house.

Funny story, ironic, and true. When I was a young man right in my late teens, and 20's when I was single, I use to visit family up there (aunts, uncles, cousins) in Saskatoon and Moose Jaw. I went in mid to late Fall to get laid and have fun. It was so fricking easy to get laid. All you had to do is go to any local bar any time day or night. All of them filled with women looking to lay pipeline. Some of you may be saying WTF right. But you Canucks know exactly what I am talking about. Come first snow all the men quit their jobs to go ice fishing and hunting for the winter leaving the Hen House unguarded. The Hens go to the Hen House (bars) looking for fresh meat. My Okie/TX accent would make bras and panties fall right off. To top it off, we rarely ever had to buy a drink or a meal.

Also seems to work pretty good in Minnesota and Wisconsin.

Oh the irony and to be young again.

[MikeCanuck]

Beer and ice fishing -now you're talkin!! Gotta have the right priorities in life. Expensive batteries can wait til the canuck dollar gets back to parity with the greenback, then I'll be heading over to a cross border costco

[Sunking]

Beer and ice fishing -now you're talkin!! Gotta have the right priorities in life.

Yep you are a Canuck.

[MikeCanuck]

PNjunction re: Be careful with auto-parts store chargers!

I just re-read your sticky about this, so looks like I was planning go down the path with a new set of batteries and an auto store smart charger you warned not go down
If I'm understanding your sticky correctly, the problem is that my 0-12A can tire smart charger may be too aggressive in applying too high a voltage to a brand new set of batteries during absorb phase? And this may shorten the battery life right from the start?
I looked in the manual for my charger, and of course it doesn't tell me the voltages it applies for each phase.
I'm going to try to get that info from can tire but not holding my breath. My junk battery may also help me here, I'll partly drain one and put the smart charger and measure the voltages applied at each phase to get some idea if it applies too high voltage after reaching 90%.
I knew that big display voltmeter I crimped to battery clamps would come in useful someday for something other than getting soc

Initial Test#1: voltmeter showing flooded lead acid auto junk battery at 12.7V with nothing else connected. Then I connected the smart charger which shows "90%" and it kicks the battery right off the bat with 14.8V for about 3 minutes with charge light blinking charging at .7A. I'm guessing this is bulk or absorb or maybe likely eq? After the initial 3 mins at 14.8v, it drops to 13.6V with charge light stopping and 0.0A charging then blips to 0.1A once in a while still at 13.6V- I guess this is absorb or trickle? In past I would need to keep the charger on this stage at least overnight to get battery from "90%" to "FUL". This time it took about an hour to get to FULL, since I was maintaining this battery with my junky 40watt solar panel so it was already mostly full to start with. After FUL, voltmeter still reading 13.6v so I guess that is float.

SO... do you think 14.8V/13.6V is too high? It doesn't seem too high except that initial 14.8V kick...

I'll do a more thorough partly drain and charge test when have time just for fun..

[Sunking]

Initial Test#1: voltmeter showing flooded lead acid auto junk battery at 12.7V with nothing else connected.

That means your battery was @ 100% SOC assuming it was rested with nothing connected.

Then I connected the smart charger which shows "90%" and it kicks the battery right off the bat with 14.8V for about 3 minutes with charge light blinking charging at .7A. I'm guessing this is bulk or absorb or maybe likely eq?

Close to correct and good enough for your understanding. What it is really telling you is what you should have already known when you seen 12.7 volt open circuit voltage, the batteery was already fully charged up. What you seen was the voltage shot right up past Bulk and Absorbed stage because the battery was already charged up

After the initial 3 mins at 14.8v, it drops to 13.6V with charge light stopping and 0.0A charging then blips to 0.1A once in a while still at 13.6V- I guess this is absorb or trickle?

Wrong it was the 3rd and Final Stage of FLOAT. Again it just means the battery was fully charged up when you started, and your charger knew it and went to Float Mode and will stay in Float indifferently. Your charger did exactluy what any good 3-stage charger will do.

You have a 3-Stage Battery charger. The whole purpose of a 3-stage Charger assuming they are sized correctly (your job, not manufacture) is to charge a battery as fast as possible. That i snot necessarily a good thing. To do its job the charge rate must be fast enough to generate some gassing at the end of the charge, an dnot be so high that it gasses the batteries during the whole charge. It is your job to make sure the charger is sized concretely, not the manufactures job. They do not know what size your battery is.

OK 3-Stage charging has 3 stages DUD! Just in case you are fishing and drinking beer Canuck!

Stage 1 is BULK and is a Constant Current mode aka CC. As the CC name implies the current is constant without any respect to voltage. The voltage is just a byproduct of current flowing into the resistance of the battery. Bulk mode is terminated when the battery voltage reaches a set point voltage. That voltage varies depending on manufacture and battery type. Good chargers will allow you to set it to what ever you want. Cheap ones like uni-taskers Optima and you have is set and you cannot change it. Some may have a switch that allows to set for Gel,
AGM, or FLA which is OK, but not as good as one you can set to whatever the battery manufacture spec. Brand A FLA battery is not the same as brand B FLA. Anyway Bulk set point is roughly 2.35 to 2.6 volts per cell or 14.1 to 15.6 volts on a 12 volt battery.

2nd State is Absorb and is just a fancy name for Constant Voltage aka CV. This can get people confused because they think the Voltage has shall be what it is set to. That may or may not be the case. All battery chargers even solar have a Current Limit or maximum amount of current they can deliver. That current limit just happens to be the Bulk current of the Constant Current phase. They do not understand that the voltage of a charging/discharging battery is a product of the Current, Resistance, and Open Circuit Voltage of the battery. Initially when the Absorb Stage is started, you will see CC mode just like Bulk. That will continue until the battery voltage rises to the Absorb set point voltage. Once reached the current begins to Taper Off and continues to taper off toward 0 amps. When charger Voltage and battery voltage are equal current stops flowing. OK Absorb Set Point Voltage is usually higher than Bulk set point. The question is when does Absorb period end???? Technically the battery is fully charged (any battery type like NiCd, Lithium, Lead Acid) when Charge current tapers down to .03C. Realistically that is BS. Unless you have a charger that is fully programmable is just jibber jabber baby talk non-sense. You are just in the Ball Park of being fully charged. Having said that don't worry about it because it is of NO CONCERN to you if you have a commercial made AC powered 3-Stage Charger. Because when Adsorb cycle ends Float Begins.

3rd Stage is Float and Float just like Absorb is a Constant Voltage. Only difference is Float Voltage is lower than Absorb voltage. Float is where you reach 100% fully charged and the battery becomes fully saturated. On a 12 volt lead acid battery depending type (Gel, AGM, FLA) and alloy (pure lead, calcium, antimony) will range from 13.1 to 13.8 volts. When you switch from Abord to Float charge current drops off the cliff, and will hold that small SATURATION CURRENT until the battery is SATURATED and fully charged up. When that happens charge current almost comes to a stop and what current does flow is the battery self discharge current. You keep the battery on Float indifinetly keeping it 100% charged up waiting to be used. So as you can see Bulk and Absorb are just sales gimmicks. The advantage is it is faster than Float alone. But that is not a good thing in itself.

Commercial and Industrial users do not use 3-Stage charging because it is too hard on batteries. They use FLOAT chargers, and the chargers are sized to match the battery of roughly C/8. Float just takes a little longer, but a much kinder and gentler machine gun to kill your batteries with a slower death, the kind you want to use on your enemy, a gut shot. You want them to suffer as long as they can before dying. Save the head shot for your sick dogs or livestock

[MikeCanuck]

Stage 1 is BULK and is a Constant Current mode aka CC. As the CC name implies the current is constant without any respect to voltage. The voltage is just a byproduct of current flowing into the resistance of the battery. Bulk mode is terminated when the battery voltage reaches a set point voltage. That voltage varies depending on manufacture and battery type. Good chargers will allow you to set it to what ever you want. Cheap ones like uni-taskers Optima and you have is set and you cannot change it. Some may have a switch that allows to set for Gel,
AGM, or FLA which is OK, but not as good as one you can set to whatever the battery manufacture spec. Brand A FLA battery is not the same as brand B FLA. Anyway Bulk set point is roughly 2.35 to 2.6 volts per cell or 14.1 to 15.6 volts on a 12 volt battery.

2nd State is Absorb and is just a fancy name for Constant Voltage aka CV. This can get people confused because they think the Voltage has shall be what it is set to. That may or may not be the case. All battery chargers even solar have a Current Limit or maximum amount of current they can deliver. That current limit just happens to be the Bulk current of the Constant Current phase. They do not understand that the voltage of a charging/discharging battery is a product of the Current, Resistance, and Open Circuit Voltage of the battery. Initially when the Absorb Stage is started, you will see CC mode just like Bulk. That will continue until the battery voltage rises to the Absorb set point voltage. Once reached the current begins to Taper Off and continues to taper off toward 0 amps. When charger Voltage and battery voltage are equal current stops flowing. OK Absorb Set Point Voltage is usually higher than Bulk set point. The question is when does Absorb period end???? Technically the battery is fully charged (any battery type like NiCd, Lithium, Lead Acid) when Charge current tapers down to .03C. Realistically that is BS. Unless you have a charger that is fully programmable is just jibber jabber baby talk non-sense. You are just in the Ball Park of being fully charged. Having said that don't worry about it because it is of NO CONCERN to you if you have a commercial made AC powered 3-Stage Charger. Because when Adsorb cycle ends Float Begins.

3rd Stage is Float and Float just like Absorb is a Constant Voltage. Only difference is Float Voltage is lower than Absorb voltage. Float is where you reach 100% fully charged and the battery becomes fully saturated. On a 12 volt lead acid battery depending type (Gel, AGM, FLA) and alloy (pure lead, calcium, antimony) will range from 13.1 to 13.8 volts. When you switch from Abord to Float charge current drops off the cliff, and will hold that small SATURATION CURRENT until the battery is SATURATED and fully charged up. When that happens charge current almost comes to a stop and what current does flow is the battery self discharge current. You keep the battery on Float indifinetly keeping it 100% charged up waiting to be used. So as you can see Bulk and Absorb are just sales gimmicks. The advantage is it is faster than Float alone. But that is not a good thing in itself.

Commercial and Industrial users do not use 3-Stage charging because it is too hard on batteries. They use FLOAT chargers, and the chargers are sized to match the battery of roughly C/8. Float just takes a little longer, but a much kinder and gentler machine gun to kill your batteries with a slower death, the kind you want to use on your enemy, a gut shot. You want them to suffer as long as they can before dying. Save the head shot for your sick dogs or livestock

Facinating!!! This explains perfectly what I saw for Test#2:

I drained the battery to 12.1V 50%soc with my 12v halogen light that I use to generate load for testing my solar setups.
Unplugged everything except voltmeter.
Connected my smart charger
Stage 1: Bulk I saw...
It started charging at 12.7V and 3A.
Over course of first few minutes, it when from 12.7V, 12.8V, 12.9V but kept charging at 3.0A.
Over course of about an hour, voltage kept increasing until it reached 14.7v and still 3.0A constantly until reaching 80%soc.

Stage 2: Absorb I'm seeing...
At 14.7V charger showing 80%soc and then starts dropping the previously constant charging from 3.0A...2.9A..2.8A,
while 14.7V remains constant.
At 90% it is now 14.8V and 1.7A charging and dropping, similar to what I saw in Test#1 at this stage.

Stage 3: Float (not at this stage yet) but I suspect it will be like Test#1 where it will drop the voltage from 14.8V to constant 13.6V and charging amps will be 0.0A.

Wow fun stuff!!

SO...my big question is... this 3-stage puppy I already have, based on how it behaves above, will it cause any noticeable battery life reduction when I bring home my 2 new FLA marine batteries, charge them up full, connect them in parallel, and keep it on float and excercise them with my halogen light and charger every few weeks for storage until needed in a power outage? Do I still need to ask mrs. santa for another $145 charger and get an earful, or am I good enough with this one I have?

Thanks ALOT guys...

[Sunking]

SO...my big question is... this 3-stage puppy I already have, based on how it behaves above, will it cause any noticeable battery life reduction when I bring home my 2 new FLA marine batteries, charge them up full, connect them in parallel, and keep it on float and excercise them with my halogen light and charger every few weeks for storage until needed in a power outage? Do I still need to ask mrs. santa for another $145 charger and get an earful, or am I good enough with this one I have?

I am too lazy today to go back and read. What size is the charger and batteries? Once fully charged up, A simple Trickle Float charge can keep them charged up. To get them charged up you want the charger to be at least C/12 with c/10 being perfect. Where C= battery AH capacity. So if you have a 100 AH battery you want your charger to be no smaller than 8 amps, with 10 being perfect. On the high end you want to keep th echarge current to C/8 or less. or about 15 amps on a 100 AH battery.

So you tell me. Are you in the right range of C/8 to C/12?

[PNjunction]

From a simplicity standpoint, and since the Noco is on sale, I'd suggest going no lower than the 7200 or better yet, the 26000, even if they are the "gen 1" models. Anything lower than the 7200 means we are treading into the difference between a "maintainer" and a charger. Too low a current on a large battery, and it may have trouble just finishing absorb, and merely timing out, or doing an endless absorb, which is not good either.

I don't know why the Gen2's are only seen at Amazon, yet the manufacturer's major site has no mention of them.

Thing is, the Noco allows you a bit of manual control, even since they are primarily automotive chargers with a float-mode monitoring, and relatively accurate voltage limits. They are relying on there being some sort of parasitic drain pulling the battery down triggering the float charge. With no drain, you have another option if you want to do a manual float to really finish:

With the 7200 and higher, there is a 13.6v "supply / maintenance" mode, but you have to activate that manually. So, first let the charger do it's normal thing. Pick your normal voltage depending on manufacturer spec (14.4 normal or 14.7v cold/agm) 14.4v normal CAN be used on agm's that spec that as the top limit, like my Exide Edge AGM does too, but in freezing weather, then the 14.7v might be a better idea and let them charge.

Once charge is finished, you can manually float them at 13.6v. This requires you to pull one of the clamps, hold the mode switch for a few seconds to get it into the supply mode, TURN YOUR FACE AWAY FROM THE BATTERY, and reattach the loose clamp.

The supply mode does not have any spark / short circuit protection like the normal charge modes do, so that is part of the reason for the shop-teacher safety awareness.

Allow the 13.6v mode to charge for at least 48 hours. As a consumer item, I'm not sure if the supply mode is rated for 100% duty, like in years. Soooo - do a charge, then 48 hours of manual float, and then every month or so put it into float mode and reattach for 12-48 hours.

Of course if you discharge it, then do a full charge no matter what.

You can see how you can play with the Noco a bit to get a better charge with some manual control if you like. But, with your large bank, don't go any smaller than the 7200.

[MikeCanuck]

Well, I'm getting two group 27 marine walmart batteries.
The thing with walmart batteries here is that they don't tell you the amp hour @20hr rate, they use "@1A rate" to make the amp hour look bigger than it is.
They are 120 amp hours each @1A rate, basically meaningless so I am assuming it is really 80 amp hours each, maybe 90.
If I charge them individually, then yes my 0-12A charger can do C/8.
When 2 in parallel, then no, but I just need to do float when they are connected parallel...

Since the noco genius G7200 is on sale this week here for cad$99, I'll look carefully at that see if christmas is coming earlier, thanks..

[Sunking]

They are 120 amp hours each @1A rate, basically meaningless so I am assuming it is really 80 amp hours each, maybe 90.
If I charge them individually, then yes my 0-12A charger can do C/8.

You are correct in saying the 120 AH is misleading. But so is the 20 AH rating.. However if you know how to apply Peukert Correction Factor you can get close.

Allow me to demonstrate. Rolls i sone of the most trusted batteries out there and they give you a great deal of information and Peukert information . All good manufactures will give you some useful Peukert info. Th ebest just ivee you the discharge curevees, but none you will ever buy does that. Strictly commercial batteries. So take a look at a Rolls 24HT-80 a Type 24 battery of 12 volts @ 80 AH. Take a look at the Discharge rates. That same battery is 106 AH at the 100 hour discharge rate, and a 29 AH battery at the 1 hour rate. So 80 AH @ 20 AH is just as deceiving. The truth takes a chart and knowing what discharge rate you will be operating at.

From years of collecting battery data I can tell you with a fair amount of certainty a correction factor 120 hours to 20 hours is roughly 1.5. So 120 AH / 1.5 = 80 AH. At 1 hour you have roughly a 25 AH battery. Pick the lie you like best.

Take any of those batteries out to the ice house and cut that in half.

[MikeCanuck]

sunking
re: From years of collecting battery data I can tell you with a fair amount of certainty a correction factor 120 hours to 20 hours is roughly 1.5. So 120 AH / 1.5 = 80 AH.
thank-you sir! now at least i'm not guessing at what it is...


PNjunction:
merry christmas to me, i picked up a G7200 on sale and lo and behold it says "lithium" on the box, nothing about gen2, but i guess that's what it is
it's in my trunk, now i just need to sneak it past the mrs....

re: first let the charger do it's normal thing...
...Allow the 13.6v mode to charge for at least 48 hours...do a charge, then 48 hours of manual float, and then every month or so put it into float mode and reattach for 12-48 hours. Of course if you discharge it, then do a full charge no matter what.

Yep I see that "13.6v supply mode" option...
I wanted to make sure I'm ABSOLUTELY clear on exactly what you wrote above, so I don't screw this up..
So here are my detailed steps - please correct if I've missed anything?

1) bring home 2 new 80ah marine FLA batteries

2) charge them INDIVIDUALLY by doing this to each one:
a) let the charger do it's normal thing
b) when normal thing is finished, set to "13.6v supply mode" and charge it an ADDITIONAL 48 hours on this mode
c) after this, disconnect the charger

3) then I connect the 2 batteries in parallel, it will always be in parallel from then on

4) every month, set to "13.6v supply mode" again and charge it for 12-48 hours on this 13.6v supply mode.
I will connect charger positive to one battery and negative to the other so charging goes across the 2 batteries evenly

5) when I "exercise" this battery bank ie. bring it down to 90% soc or so, and with batteries still in parallel, I would:
a) connect load positive to one battery, negative to other so discharge is even across both, disconnect load when done
b) connect charger to one battery positive and other negative, do normal charge, then additional 48 hours on "13.6v supply mode", then disconnect
c) check and top off distilled water

yes?

thanks again..