“The bigger concern is whether you’re deep-cycling batteries that are not intended to be deep-cycled. If you are, you’ll get about 3 to 5 cycles out of them and then plates will start to disintegrate.”
-
Does immediate re-charge help mediate that?
Is there a percentage de-charged (for example on a 12-volt battery, down 25 percent percent to 9v remaining?) at which point the damage goes logarithmic?
ping
For pete sake. According to the Battery FAQ posted just before your post, that 25% SWAG I used as an example was right.
I pretty much totally pulled that out of thin air, after watching the voltage on my first attempt to boil water - I could see the power delivery to the hotpot drop significantly about that point.
At 75% of capacity, sulfation begins. Lots of information here...
“Is there a percentage de-charged (for example on a 12-volt battery, down 25 percent percent to 9v remaining?) at which point the damage goes logarithmic?”
I’m not sure what a good number is for lead acid battery that’s not meant to be deep-cycled is, but I don’t see 25% as a problem. So if your battery is 10 Amp-hrs, you pull out 2.5 Amp-hrs, so you have 7.5 Amp-hrs left.
A bigger problem (from what you wrote) is that you’re trying to use voltage rater than Amp-hrs to determine battery state of charge. Don’t do that. Voltage generally will not drop much until the battery is almost depleted. In other words, you’re probably 90% drained by the time you see 9 Volts. You pretty much have to measure how much energy you’ve pulled out of the battery, rather than look at voltage.