IMO the
reach and
maintain approaches require different levels of heat
- reach is seen with self-heating batteries that wait for charging to do their work. The batts are allowed to freeze (overnight, typically) then are heated when charging power becomes available. If we want to start actual bank charging in a reasonable amount of time firmer heating must be applied.
- maintain is seen with external warming setups. The minimum temp is held constantly so the batts are never allowed to freeze. This is not a time-limited operation so warming can be gentler.
Example: I keep 150Ah of LFP at 50F in ~freezing temps with 16w warming pad underneath. The pad gets slightly warmer than body temp if set out with nothing touching it. I do snowbird to avoid hard freezes, but still got caught in a 19F ice storm once. The temp controller was still cycling the mat off regularly to avoid exceeding the 50F setpoint. This suggests it could have handled colder conditions even if I (and the plumbing) couldn't.
SOK's self-heating appears to be "4A for each 100Ah battery, 7A for each 206Ah battery" (
source). Extrapolating from that we might say ~70W for on-demand heating a 150A bank like mine.
I suspect the choice is one of preference or convenience for the average LFP owner. People scrapping for every watt (offgridders, boondockers, etc) might find one or the other best suits their use case. I threw together
a few thoughts on the matter elsewhere. Horses for courses, pick your poison and all that.
