I'm already apologising...

[MichaelK!]

Ok, now I'm getting some understanding, finally lol

This is interesting,
,
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If you look at the data for Odyssey AGM batteries, you find that they are good for 630 discharges to 50% but only 400 discharges to 80%. Seems obvious that the 50% depth of discharge (DoD) is better. But hang on, if you flatten your batteries to 80% DoD, you won't have to do the recharging as often, so fewer cycles. The important parameter is your lifetime capacity in Amp-hours, which you get by multiplying the battery capacity * DoD * number of discharges. For a 225 Ah battery, your lifetime capacity is 71,000 Ah if discharged to 50%, but is 72,000 Ah if discharged to 80%. Indeed, If you look at Odyssey's data for 100% DoD, you still get 72,000Ah of lifetime capacity! For Odyssey batteries, there is absolutely no reason to worry about your DoD, you're not gaining anything by starting up that generator when your battery gets to 50%.

######################

The problem with mathematics like this is that it implies that you are controlling the cycling of the battery. In fact though, most likely you are not. The daylight is controlling the cycling. Most battery manufacturers define a cycle as the time between two full charge events. That most likely would almost always be sunset of day one, to sunset of day two.

Let's say hypothetically that you drain 40% of your battery capacity each and every night. The next day, the panels will automatically try to bring those batteries back to full charge (we hope). So, let's say you connect your new batteries on Monday morning. By Friday, the batteries would have gone through 4 complete cycles. The only way you could get the batteries drained to 80% is if you disconnect the solar input on Tuesdays and Thursdays. I don't know one single person that actually disconnects their panels to encourage deeper discharges.

I think the issue of sulfination far outweighs the gleaning of every single amphour you can get out of a battery.

[velo27]

I've just got a multi meter and tested the batteries, they read at 13.33v & 13.44v @99% charge, being a sunny day...

Going to retest at 50%

At 60% readings are 13.1 & 13.2.. And the system has run well today even though overcast... Ran the deep freeze all day on it and stayed at 99% till about 3:30pm and then started dropping, and at 6:30pm it's down to 55%, I'll turn off the inverter now...

Maybe the fact I disconnected the entire system and reconnected has made a difference, perhaps a loose connection?

[Mike90250]

That's the reason I often suggest an initial system uses cheap golfcart (2 year) batteries, you sacrifice them instead of the top of the line batteries

[velo27]

Ok, now I'm getting some understanding, finally lol

This is interesting,
,
################################
If you look at the data for Odyssey AGM batteries, you find that they are good for 630 discharges to 50% but only 400 discharges to 80%. Seems obvious that the 50% depth of discharge (DoD) is better. But hang on, if you flatten your batteries to 80% DoD, you won't have to do the recharging as often, so fewer cycles. The important parameter is your lifetime capacity in Amp-hours, which you get by multiplying the battery capacity * DoD * number of discharges. For a 225 Ah battery, your lifetime capacity is 71,000 Ah if discharged to 50%, but is 72,000 Ah if discharged to 80%. Indeed, If you look at Odyssey's data for 100% DoD, you still get 72,000Ah of lifetime capacity! For Odyssey batteries, there is absolutely no reason to worry about your DoD, you're not gaining anything by starting up that generator when your battery gets to 50%.

######################

[chrisski]

17% is low? OK, but they are deep cycle AGMs... I got no idea... I hope they aren't toast

So I thought AGMs could only go down to 60%.DoD. Google tells me, its 80% DoD. There's a Trojan white paper that says Discharging below 80% DoD could damage internal components. How much at 17%, only 3% below, I don't know.Trojan_QSG_AGM.pdf (trojanbattery.com)

Here is a Trojan AGM Depth of Discharge vs Cylce Chart:

AGM DOD vs Cycles.jpg

[velo27]

I've just got a multi meter and tested the batteries, they read at 13.33v & 13.44v @99% charge, being a sunny day...

Going to retest at 50%

[velo27]

17% is low? OK, but they are deep cycle AGMs... I got no idea... I hope they aren't toast

[chrisski]

We were awoken about 2am a couple of weeks ago to the inverter alerting us to low battery charge, it was 17%, I assumed the charge controllers job was to protect batteries from these situations... I haven't touched any settings on the controller as I was informed by my supplier (who has zero after sales service) that it came preset...?

I'm pretty sure 17% is too low for AGM. With FLA, the limit is 50%. Lithium you could be fine.

The charge controller normally will not protect the battery. My Victron does have an option to control a relay which I guess you could put in line somewhere to trip a certain voltage, or at least shut off the inverter. Honestly though, my watt hour sucking loads are on the DC side.

The inverters I am familiar with have a low-voltage cut off. Mine is 10.5. Too me, that is much too low for battery health. No inverter I looked at had an adjustable low voltage cutoff.

All I have is a battery monitor which has an audible alarm that will go off at a state of charge I set it to. Has an option for a relay, but I don't use that. I am on my bluetooth many times throughout the day.

My guess is those batteries are toast. With AGMs, the only thing you can do is put test them with a multimeter, put them on a charger, or perhaps a load test at a parts store.

[velo27]

All you can do is measure them with a multimeter. Other than that, depending on the battery, a local parts store may be able to load test it. If they do, take the results with a grin of salt. The tester is after all built for car batteries.

What’s the lowest you read SOC and how often?

Also could be something else like a bad SCC, but that’s where troubleshooting happens.

We were awoken about 2am a couple of weeks ago to the inverter alerting us to low battery charge, it was 17%, I assumed the charge controllers job was to protect batteries from these situations... I haven't touched any settings on the controller as I was informed by my supplier (who has zero after sales service) that it came preset...?

[chrisski]

All you can do is measure them with a multimeter. Other than that, depending on the battery, a local parts store may be able to load test it. If they do, take the results with a grin of salt. The tester is after all built for car batteries.

What’s the lowest you read SOC and how often?

Also could be something else like a bad SCC, but that’s where troubleshooting happens.

[velo27]

The whole system is only 3mths old, I really hope things aren't nearing the end of their life cycle, these batteries cost loads

[chrisski]

To me equalization never seems like a good idea with other than FLA batteries.

The one time I equalized my batteries, they were bubbling so much it sounded like a small river. This is the water breaking down. With FLA, you can always add more. AGM you can’t.

The electrolyte in an AGM battery is like a gel. That’s why they can be turned on their side. AGMs shouldn’t vent except at the end of their lifecycle and then it’s time to change them. The gel like electrolyte is also why you just can’t add water to replace it.

If the owners manual says different, follow that.

[velo27]

Before you equalize, you have AGM batteries. As far as I know, equalizing on AGM batteries is a big no-no. Flooded lead acid is fine, but not AGM.

Yes, a quick Google has me getting conflicting information regarding equalisation of AGM, seems to be specific to manufacturers requirements....

I've also just discovered a device, I'm thinking of purchasing called a 'battery equaliser' that ensures equal charging to both batteries, seems like a good idea?

[chrisski]

Before you equalize, you have AGM batteries. As far as I know, equalizing on AGM batteries is a big no-no. Flooded lead acid is fine, but not AGM.

[velo27]

Thx for the responses... Sounds like I'm experiencing normal reduction in performance for the time of year, just didn't expect it to drop so quickly... I'm going to need to add a wind turbine by the sounds of it, cause we have an abundance of wind here.

Never done an equalize charge, so will try that...

Both batteries are measuring 12.8v output, so I guess that's positive..