why i call Li fussy

2oldman wrote:

PerryB67 wrote:
Does Battborn, Renogy, etc. have a LFP battery with a heater that can sit for months without charge, without the built-in heater running, and then two days before leaving can you turn that heater on?

LFPs can sit for a long time without being charged. Since the heater only draws 1.8a, and is very smartly controlled, yes.

What is that "1.8a" for how long?

FWC calculated 10-15% of battery capacity to heat it up from -20C to +5C with 125W in an hour, so that would be 12.5 DC amps with an inverter. The 120v charger doing the heating first would be at say 55 amps or whatever the heater "accepts" --not clear on that. Anyway 1.8a DC does not seem nearly enough.

Perry can start the furnace and has 12v on arrival at the storage at -20C, since nobody said the LFPs are dead or at BMS shut down. You can draw from them down to minus whatever, but can't charge them.

So you would need say 20AH left in (usually stored at 50%?) to run the furnace and lights etc before getting some charging going somehow (scenario?-- take the rig home to load it up and while there plug into the stick house? Generator? Solar? )

That 20AH would be a higher percentage of the capacity at -20C than at +5C so storing at 50% would leave enough?

It is true you can organize things to operate in those temps down to the -20s but not down to PT's worst case scenarios AFAIK. I think he is right to say they are "fussy", especially in the mystery temp range 0-5C where you should use "reduced charging amps". That does not mean they are bad just fussy. Other batts have their own ways of being fussy--eg charging AGMs to 0.5a/100AH.

IMO Perry made a good choice and does not need to second guess himself for his scenarios. There are conflicting info/opinions on all this low temp stuff, so hard to tell what is Gospel. If you don't have LFPs then no worries! Or if you do, there is always, "What, me worry?" to go by. :)

Reduced charging amps at 3C would be a problem for me where it would then take too long to recharge the bank using the generator. Can't run the gen all day. If it never got above 5C, it would be doom for getting through the next night. Have to be able to charge at full amps from the start.