Originally Posted by Too Tall
...Question: So if I'm dry camping and discharging to say 60% and bringing the charge back up to maybe 80% each night with the generator (due to time constaints) Is that going to decrease the life of the batteries? Once I get home should I do a high rate charge as you described to bring them back to a storage level? thanks.
Good question and from what I can tell, discharges like that are not a problem.
Strangely, considering that flooded cells have been around for a long time, there are still some mysteries. When you discharge a lead acid battery, lead sulfate begins to form on the plates. This is a normal and reversible process and the sulfate will go back into the electrolyte when you charge again. It seems that for a while the sulfate is amorphous (no crystals) and is easily dissolved again on charging. When you deep discharge a battery there is an increased probability that this sulfate will form crystals and they are harder to reverse than amorphous sulfate. Hence when you go over 50% you will begin to form crystalline lead sulfate and some of this may not go away on recharge. When that happens, the battery permanently loses capacity. You can measure a good resting voltage but when you try to draw current the voltage will drop more rapidly as the cells don't store as much charge as they first did. One thing that is pretty well accepted though is that if you do go beyond 50% don't leave the battery in that state for very long. Immediately recharge it!
As a result, the normal 10,20 or even 40% discharge cycles should not have a permanent effect on the battery. Charge it back whenever. I did mention that without a Trimetric you don't know any of this stuff and with one you will start to get into information overload. I have 4-12 volt batteries in my rig and I told the Trimetric that my bank is 400 AH, which is conservative. Remember that the meter is only counting discharge current integrated over time. If you tell it your bank is larger than it is, it will give you a false sense of security on SOC. Electron counting is the only way it is working and while it tells you the voltage it really isn't doing much with that.
But at least you aren't looking at 4 red LEDs and trying to figure out how much reserve you have left and if you should start the generator and you aren't measuring resting voltage and looking at a chart either.
Now all of this is pretty well accepted. Beyond this there are snake oil treatments, ultrasonic de-sulfation and a whole bunch of other potential magic. Finally, there are some who add a couple of ounces of mineral oil to each cell and swear by it. Mineral oil does make sense and I think they may be right but I haven't decided to try that yet on my batteries, but I think I will get there.