danderer
Guru
Apologies in advance if this is common knowledge but I just figured it out.
I've got a house bank of 1000 Ah of Rolls AGM batteries which means 500 Ah usable. I don't let the batteries go below 50% but it is a pain when the batteries approach this figure at the end of a day. What to do? Run the generator a couple hours (most expensive electricity ever) or let the batteries go below 50% (and shorten their lives) and just charge them from the main on the next days run?
I stumbled on a post suggesting that pulling the batteries below 50% wasn't that big a deal - https://tab-rv.vanillacommunity.com/discussion/9940/agm-battery-depth-of-discharge-myth-busted I then dug into the Rolls data sheets.
My Rolls AGMs list an expected life of ~1200 cycles at 50% depth of discharge. That translates to 1000 * .5 * 1200 = 600K Ah. At a routine 80% DOD the expected cycles drop from ~1200 to ~675 cycles - almost a 50% decrease. However, the usable Ah in this case are 1000 * .8 * 675 = 540K Ah. That is just 10% less than the 50% DOD number. Looking at total Ah available rather than cycles suggests that going below 50% DOD occasionally - or maybe regularly - isn't that big a deal.
Another conclusion I've reached from this is I spend too much time worrying about the batteries. I'm just going to use them as I want (within limits) and replace them when needed.
I've got a house bank of 1000 Ah of Rolls AGM batteries which means 500 Ah usable. I don't let the batteries go below 50% but it is a pain when the batteries approach this figure at the end of a day. What to do? Run the generator a couple hours (most expensive electricity ever) or let the batteries go below 50% (and shorten their lives) and just charge them from the main on the next days run?
I stumbled on a post suggesting that pulling the batteries below 50% wasn't that big a deal - https://tab-rv.vanillacommunity.com/discussion/9940/agm-battery-depth-of-discharge-myth-busted I then dug into the Rolls data sheets.
My Rolls AGMs list an expected life of ~1200 cycles at 50% depth of discharge. That translates to 1000 * .5 * 1200 = 600K Ah. At a routine 80% DOD the expected cycles drop from ~1200 to ~675 cycles - almost a 50% decrease. However, the usable Ah in this case are 1000 * .8 * 675 = 540K Ah. That is just 10% less than the 50% DOD number. Looking at total Ah available rather than cycles suggests that going below 50% DOD occasionally - or maybe regularly - isn't that big a deal.
Another conclusion I've reached from this is I spend too much time worrying about the batteries. I'm just going to use them as I want (within limits) and replace them when needed.