Originally Posted by 2martins
what if you have AGM batteries?
I am looking at some 200 amp hour 6 volt AGM batteries from wholesalebatteriesdirect for $220 each it seems like this is a good deal for AGM and 200 amp hours compared to the more common FLA 6 volt providing 100- 105 amp hours at $110 each with 10% off for p/u in store at batteriesplus. BUT, one site says the amp hours are for the cheaper battery is 230 amp hours *for 20 hour* Is that the same standard that is used to measure the amp hours of the FLA batteries? They weigh about the same amount, which makes me question that.
You should be able to find 200-220A/H 6v FLA's for $85-$130.
Sam's Club has GC2's for around $85 and Trojan T105's can be had for around $130.
Regarding SOC of AGM's. I don't know the answer to that question. A quick Google search yielded:
State Of Charge (SOC) for AGM Batteries
It will be pointed out that SOC can only be measured by voltage when the battery bank has been at rest for at least 3 hours. At rest means not being currently charged by a charger/solar panels or discharged by devices attached to the battery bank. Being at rest will allow the batteries to stabilise and thus give a more accurate reading when measuring by voltage.
For greatest life the battery bank should not discharge less than 50% SOC
100% SOC 12.8 volts or greater
90% SOC 12.7 volts
80% SOC 12.6 volts
70% SOC 12.50 volts
60% SOC 12.30 volts
50% SOC 12.20 volts
40% SOC 12.00 volts
30% SOC 11.80 volts
20% SOC 11.70 volts
10% SOC 11.50 volts
0% SOC 10.50 volts
This assumes a 12 volt battery bank. Double their numbers if you have a 24 volt battery bank.
Yes, you want to be looking at the 20hr rate when sizing/comparing batteries.