[john61ct]

First off, put in good temp sensing

then insulate the pack well.

Thin custom silicon heating pads with built-in thermostats can be ordered cheap from china, when things get back to normal.

eBay would be first stop

 

[john61ct]

Obviously, **if** through normal usage the internally generated heat gets them warm enough so normal charging rate is not dangerous, fine and good take advantage of that.

But any explicit intentional warming done for that purpose, should be applied from ambient warming from outside the battery casing.

Do **not** apply or draw current for that purpose, generating heat that way **will** reduce lifespan.

I agree if there are sound fluid circulating channels built into your packs it would make sense to re-use them if practical.

 

[john61ct]

custom heater pads can be made whatever voltage you like

the included thermostat should be for high-temp cutoff IMO, use your own regulation for normal ops.

Space between the pad and cells, warm the air inside an insulated box.

but using built-in liquid jackets is ideal if you can