profdant139 wrote:
If storage at 50% state of charge is optimal, I guess I can't just put a lithium battery on a shelf in my garage hooked up to a BatteryMinder Plus (which is what I do now with my lead acid dinosaurs). Dumb Question Number 17 -- if I can't leave a lithium battery on a trickle charger, how do I keep it at 50% while it is in storage?
And by "storage," I mean "whenever I'm not actually on a camping trip, the batteries go onto the trickle charger."
Thanks to everyone for your continuing patience with my naive questions -- judging by the little "hit counter" on the welcome screen for this forum, there are a lot of other folks like me who are curious about lithium but aren't sure what to ask.
Lifepo4 *cells* by themselves have extremely low internal parasitics. We have a 200ah 3.2v cell that I removed from a cell pack about 10 mo. ago. Voltage of the cell at the time I removed it was 3.287v. Checked the voltage last week and it was 3.285v. At this rate it could a few years to drop to 50% SOC (~3.280v).
The BMS in a lifepo4 *battery* is tasked with protecting the cells 24/7/365, and, unfortunately, needs to draw power from the cells 24/7/365 to do so. Not all BMS's (or cells) have the same parasitic draw, so the rate of (self) discharge will vary slightly from battery to battery. For long-term storage purposes, I'd suggest charging a 12v lifepo4 battery to 50% (13.13v), disconnecting everything from the terminals, then checking voltage every few months. Log the voltage drop. After a couple of checks you should have the data you need to pick the best time interval for the following voltage checks. In any event, once the voltage drops to 13.00v (30%) suggest charging it back to 13.13v (50%) again.
As 3 tons and 2oldman have already mentioned, for storage purposes, no need for a charger (unless a recharge to 50% is necessary). Charge the battery to 50% SOC, then disconnect everything from the lifepo4 battery terminals. Make occasional voltage checks as previously mentioned. Important tidbit: leaving a charger connected to a lifepo4 for long periods of time (at 100% SOC) can potentially damage the battery. 50% SOC is the sweet spot for a lifepo4 battery/cell.
