[nebulight]

There are two views about using a BMS (battery management system) to turn the charger on and off based on battery temperature:
1) One view is that a single sensor is just fine for running a control system and no back up is needed
2) Another view is that the BMS is there as an "emergency backup" in case the normal controllers such a charger, temp control, etc fail to perform correctly

At this very moment, Boeing has a whole bunch of 737s parked in a big lot because of just one instance of thinking in terms of (1)

Similarly, there are two views about the power system being on vs off when parked at an airport.

I may or may not turn off the inverter, but in general, my electrical system is designed to be turned on - and stay on.

I hear you. Design your system with multiple levels of automation. OP didn't give much detail so my suggestion was to just disconnect the battery altogether since he wasn't in the van. If you have the right type of chargers that have built in protections (Victron MPPTs have internal temp sensors but can also use external for better accuracy at the battery), you should have those to disconnect your charges well before the BMS kicks in. However if it's cold enough, the BMS will disconnect the chargers regardless of what other protections you may have in place. That's why I asked why it was a problem if the BMS disconnects. I've read some batteries like Renogy don't reset properly after a BMS disconnects so maybe that was what OP was posting about.

 

[phil]

FWIW, I was curious what they looked like.
this one has elements on both sides

this one weaves an element through each layer of cells

 

[nebulight]

This is a good design (top image). I watched that video and the heater only kicks in when there is a charge current and powers the heater for that charge current and doesn't pass it along to the battery until the battery is at temp. Then it will start charging the battery. Best implementation I've seen to date.

 

[epicsurf]

I never did implement the battery heater since I was too busy and now the second set of Renogy batteries have failed. I’m having a really hard time getting them replaced under warranty or just getting support. I wanted to buy their newer heated battery but really don’t want to do business with them anymore. I have waited on the phone for up to an hour only to be disconnected. Their support is the worst.