AGM questions about long life

[Jman]

For higher loads usually like inverter use for 3-4hours a day. On some trips no solar & on other yes, but sticking with 30%DoD rule. I have been told by folk in the RV camping world regardless that if you wan't any long life out of your AGM it's really only C/20 for AGM not C/4. Is this true?
Is life cut short from frequently charging at lower than C/4? like C/6-7. If so then how are we expected to find the right rate with fixed dc-dc chargers and fixed solar panel sizes?
Does AGM need to be frequently discharged deeply a few times if kept in long storage much of year with a CC maintaining it?

thanks

[Sunking]

I have been told by folk in the RV camping world regardless that if you wan't any long life out of your AGM it's really only C/20 for AGM not C/4. Is this true?
Is life cut short from frequently charging at lower than C/4? like C/6-7.

They are full of poop.

If so then how are we expected to find the right rate with fixed dc-dc chargers and fixed solar panel sizes?

Same as any battery by sizing your panels and controller correctly.

Does AGM need to be frequently discharged deeply a few times if kept in long storage much of year with a CC maintaining it?

Where are you getting this BS? Have you ever tried searching for answers by manufactures. Try this one and see what it says. Example:

The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle.

The second advantage of AGM is they can be discharged deeper down to 50% DOD and still obtain long life. That does not mean or imply they should be taken down to 50% DOD.

[BackwoodsEE]

Does AGM need to be frequently discharged deeply a few times if kept in long storage much of year with a CC maintaining it?

I'd be interested in some further discussion of this. My hybrid battery-backed grid-tie system keeps the AGMs in float service almost all the time. Every month or two, I disconnect it from the grid and run the batteries down to around 75% overnight. Mostly, I will confess, just to play with my big grown-up toy, but I also wonder if it makes sense to "exercise" the batteries once in a while.

Nothing I've read, here or elsewhere, has given me a strong impression about the desirability of doing that. I just figure it won't hurt to have 5-8 or so relatively modest DOD cycles every year, considering that the AGMs will eat themselves up within 5-7 years no matter how lightly they are used.

[Sunking]

I'd be interested in some further discussion of this. My hybrid battery-backed grid-tie system keeps the AGMs in float service almost all the time. Every month or two, I disconnect it from the grid and run the batteries down to around 75% overnight. Mostly, I will confess, just to play with my big grown-up toy, but I also wonder if it makes sense to "exercise" the batteries once in a while.

Nothing I've read, here or elsewhere, has given me a strong impression about the desirability of doing that.

To form the plates and abtain full rated capacity of either FLA or AGM does require cycling. How many cycles is a question of the manufacture. Example if you look at Trojans User Guide page 23 states less than 20 cycles for AGM and 50 to 100 cycles for FLA. When I questioned my Trojan rep years ago what constitutes a cycle is 25% DOD or 75% SOC.

Just keep in mind that is to FORM THE PLATES to obtain maximum AH capacity. Once done it is down hill from there and does not imply they should be deeply discharged. What can be said that is universally true of AGM and FLA is AGM can be discharged deeper than FLA where AGM can go down to 80% DOD, while FLA should be limited to 50% DOD. Again that does not imply you should, it means you can when in a pinch. Doing so will take its toll and cut cycle life. Bottom line is you are not going to find any credible source or authority of batteries that would recommend deeply discharging AGM batteries to extend battery life.

Only battery chemistry I know of that can resurrect a battery is those of Nickel primary NiCd memory effect by a slow deep discharge to 1 vpc, than a slow slow charge at C/20 rate for 30 hours or until warm.In no uncertain terms will it have rated capacity, but can make it useful again with reduced capacity.

[Sunking]

Backwoods you might be interested in reading some IEC 61427 test Trojan has ran on two of their AGM lines. Not many manufactures will perform IEC 61427 test let alone publish them if they do.

27 AGM
SAGM_6_220 aka T-105 AGM

Edit Note if you want to see the Mother of all Batteries test results here you go. No other battery chemistry be it Lithium or any other will last as long and take the beating of this battery line up. After 2400 cycles still had 103% rated capacity. Backwoods you will kick yourself because they cost less than your AGM's.

[BackwoodsEE]

Thanks for the info, Sunking . I hasten to add that I discharge to 75% SOC, or a mere 25% DOD, when playing around with the system as mentioned above. Discharging to 25% SOC would be foolish, and I'd be shutting down all but essentials and getting the generator hooked up if the grid were down and things were heading to that point.

[Bigbillsd]

This is an interesting thread. When talking to my rep from Crown battery they told me I can go 80% DOD and still get 750 cycles from their CR-260 FLA batteries. It was quite a bit more cycles for 50% DOD, I rarely get them down to 40% DOD, most of the time in the morning I have only pulled out about 150 Ah from my 520 Ah batt set. -Bill

[Jman]

Ok another thing I'm wondering about, after reading Are you killing your batteries part 2: Does AGM need the max smoke bulk at 14.8V all day? or does it apply to Flooded only?

[Sunking]

Ok another thing I'm wondering about, after reading Are you killing your batteries part 2: Does AGM need the max smoke bulk at 14.8V all day? or does it apply to Flooded only?

FLA only. No way to determine if AGM is fully charged or not.