I'm very much a 'newchum' on the subject of power requirements for life on the road, and have been devouring old postings about solar & batteries & setups. I was going to post this in reply on one of them but hesitated to do so because of the ages of the postings. So I figured to throw my "two bob's worth" in on a new posting for all those who may not be aware.
One thing I do know with absolute certainty is that, unlike lead acid batteries which deteriorate if regularly discharged below 85% capacity (yes, even 'deep cycle' batteries will not put up with it forever even though they are designed for deeper discharge cycles), Lithium Batteries deteriorate faster if regularly charged over 85% of their capacity. About once a month or so is good for them, but day to day is not. They also shouldn't be regularly allowed below around 15 - 20%. They develop dendrites (little 'veins', kind of like plant roots) internally which gradually reduce their capacity over time. They can also (in short, fast charging cycles) relatively quickly penetrate the separator between the cathode & the anode resulting in a short which will kill the cell and can even result in a spontaneous fire.
One of the posts I read the OP had a problem with his/her lithium battery only 4 years old discharging rapidly. This is possibly the cause. Some lithium battery packs can be repaired by replacing an individual cell, but whether this can be practically done with bigger batteries I don't know. I'd also hazard a guess that if the problem is occurring with a battery several years old it probably wouldn't be practicable anyway as other cells in the battery may well be getting close to the same problem.
For what it is worth.
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Some of the cheap lithium batteries are using C grade cells, so the battery is not going to be brilliant to start with.
Lead acid batteries have a total life watt/hours. If you add up the total wattage of low depth discharge, compared to high depth discharge. It's about the same total watt hours.
& the battery is not going to fall off a cliff at the end of its total watt hours.
I have 4 small lead acid batteries. Another use for them is jump starting wich I have done for other a number of times, another one a week ago! 1040 amps for 5 seconds, or 360 amps for 5 minutes.
Mostly they run the fridge which is about 15AH per 24 hours.
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50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.
... One thing I do know with absolute certainty is that, unlike lead acid batteries which deteriorate if regularly discharged below 85% capacity (yes, even 'deep cycle' batteries will not put up with it forever even though they are designed for deeper discharge cycles), Lithium Batteries deteriorate faster if regularly charged over 85% of their capacity. About once a month or so is good for them, but day to day is not. ...
I much prefer actual RV users experiences to the screeds of theory and workshop or laboratory based data out there.
Our 300Ah 4 cell Sinopoly LiFePO4 battery pack has now survived 11 years of full-time travel spending perhaps 95% of its life above 85% SOC.
According to some of those theorists we must be very, very lucky.
I capacity test the battery at C/10 each November 5.
At the last test in Ah the battery had "deteriorated" from the original 315 to just 299!
Insignificant? It is to us.
When the battery eventually fails either tomorrow or 15 years from now it will simply be replaced with whatever suitable and affordable energy source is available at the time.
Maximum 14.1V from any charge source. 12.2V battery disconnect. Never triggered in daily use.
The battery has also started the 3.9l turbo diesel truck engine a few thousand times. "BMS" circuitry is necessarily external.
Battery daily cost to date if the battery dies tomorrow= 50 cents.
Absolutely insignificant compared to other travelling expenditure.
-- Edited by Scubadoo on Saturday 9th of August 2025 10:37:15 AM
