I'm already apologising...

[velo27]

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%.

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[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]

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?

[MichaelK!]

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%.

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

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.