On Saturday, May 19, 2018 at 8:38:15 AM UTC-4, Tango Eight wrote:
On Friday, May 18, 2018 at 11:05:47 AM UTC-4, wrote:
Interesting - the discharge voltage goes down with lower temperatures - isn't that the opposite of lead-acid? At the least, lead-acid needs higher CHARGING voltages when it's cold.

How well does a microAir radio, which is finicky at low SLA voltages, do with a "12V" LFP battery, which offers a slightly higher voltage on the discharge curve?

Those voltage curves apply to 0.5C discharge, i.e. a two hour discharge rate. The primary reason for the change in behavior at low temperature is increasing internal resistance, not decreasing open circuit voltage. Compare to similar curves for SLA batteries, if you can find them (they'll probably be at slower discharge rates).

Under real world glider use, LFP batteries perform better than SLA batteries in cold conditions. But don't recharge below 0 C.

T8

The claims that one should not charge LiFePO4 batteries below 0 deg C - but charge as fast as you want at +1 C - don't make sense. I've read that there are issues at low temperatures with the lithium plating the graphite anode (or is it the cathode?) instead of being absorbed into it, due to slower reactions. OK, but then the charging rules should be something like:
* up to C/5 at 10 C
* up to C/10 at 5 C
* up to C/20 at 0 C
* up to C/50 at -5 C
but I've never seen anything like that. And "0 deg C" is too round a number to be quite correct for anything other than freezing water. What gives?