Lithium - Charging

another factor that a lot of people don't even think of when we are talking RV batteries is the charging rate.  so when cycle life is determined, by eve for example, they have the cell in compression, and they charge it to 100% at a 1C rate so my 304Ah cells are charged with 152 amps.  they charge to 3.65V/cell so 14.6V for a 12V pack at constant current and then switch to constant voltage when the cell hits 3.65V  and hold it there until the amps drop below 0.05C so 15.2A and then they consider it fully charged they rest for 30 min, then discharge with a 1C discharge to 2.5V (10V for 12V pack) let it rest for 30 min then recharge and repeat.  

when the capacity is reduced to 80% of the original that is considered the cycle life.

so if you notice they are not giving stuff much of a chance to really cool down and are charging and discharging at higher than recommended constant use, as my data sheet for my cells recommend constant charge and draw stay at 0.5C.  when I charge, even if I am plugged in and leave my solar on I am pumping 60A at most into that, if I start the truck up and add the dc to dc charger I can take that to 80A so at most I am putting in just a shade over 0.25C which means I will not be generating anywhere near as much heat so I expect we are extending my cycle life with the way it is charged and drained.  now there will always be that exception, the guy with 2000 plus watts of solar and a smaller battery bank that comes close to a 1C charge but I would say a good majority of people with lithium don't even come close to those charge rates and I think people get way to hung up on reducing operating voltage and worried about hurting the life.  the life of the battery is based off a 100% to 0% to 100% cycle so if you take care of it in other situations (cold charging, long term storage which eve defines as over 3 months, and not leaving it at 0% for extended periods of times.) you should get the cycle life stated. 

like I said in my other post the only reason I set a 10% bottom is that is where it drops below 12V and rapidly drops to 10V so for the stability of the electronics I cut this part out.  it probably won't hurt the electronics either but as voltage drops for a given 12V piece of equipment the amperage it consumes raises to maintain the same wattage rating so by limiting the lower voltages you can actually protect cheaper built 12V electric equipment as the cheep stuff will use wires that are to thin and other things.  I actually think the problem people have been having with fantastic fans burning out are more from under voltage than over.  

While I am not an expert at the care and feeding of batteries, Will Prowse is, and he points out that LiFePO4 batteries have a BMS that requires them to charge to 100% in order to balance the cells. This is essential at least with some frequency lest the cells become unbalanced. One can argue that cycling them between 20% and 80% will give you the longest life, the fact that even the roughest use is likely to have them last 10 or more years, you are going to get your money's worth out of them. Will Prowse says cycle them between 5% and 100% all you want.

The battery chemistry in you phone definitely does not like being charged to 100%, but the chemistry of those batteries in your camper is totally different.

who said you don't need them at 100%?  I do it two different ways when I am at home, with the camper I don't plug it in and adjust my custom settings on my solar controller to hold it at 70%.  a night or two before i go camping I change it back to 100%

I think to many people are getting confused with voltage for long term storage where if you are going to have no voltage in and out for 3 months then you set it down to 50 to 70% and let it set for the off season. 

when your actually using it 100% to 0% is perfectly fine that will just give you the cycle life.  the other situation is for people who use it as battery back up for their house that is on solar, they set 90% as a top charge for a bit longer life as they cycle a lot more than normal so they want to squeeze some extra cycles out of their battery.  in fact not charging to 100% long or frequent enough can be harder on the battery as they go out of balance and lower your actual capacity until you top balance them again.  with the cheep batteries that seams to be one of the most common issues, so I would charge it to 100% and hold it at a 14.4V float charge for a day or if they have blue tooth see what there actual cell voltages are and how far they are out.  Ideally they should be with in 20mV of each other

the only setting I take off the top and bottom when I am camping is I set my floor at 10%, not for any reason really aside from that's where they bottom knee is and the voltage drops below 12V

as for letting it sit the issue comes in if an equalization phase starts, if your confident that won't happen then you could switch it to lead acid when your sitting at home,  but I would switch it back to Li a few days before you go out to make sure your battery is 100%, why leave extra capacity sitting in the driveway?