Can anyone recommend a USB battery warmer to me?

I have one of those 2.5kwh portable battery packs with built in inverters.  its LiFePo4 so it handles cold relatively well but I'd like to be able to keep it above freezing in the winter. I was going to add a DC heater to one of the USB ports for that purpose.

However i am struggling to find one. Should be a USB cable to a combined heater/thermostat, that will generate heat when below a certain temp.  All my searches get drowned out with USB hand warmers and USB chair heaters which aren't what I need and lack the thermostat.

Hi @ll,

I think the reason you're struggling to find it is that you may be better off separating the thermostat from the heater.

There are small 5V USB digital thermostat controllers with an external temperature probe. You can set a start and stop temperature, then connect an ordinary 5V USB heating pad to the output.

So basically:

USB battery output → thermostat controller → 5V heating pad

Try to found it at Walmart or other similar: USB 5V digital temperature controller with a probe and programmable start/stop temperatures.

I would probably use a 7–10W heating pad, put the battery in a lightly insulated enclosure and heat the enclosure rather than putting the heater directly against the battery. Put the probe against the battery case and perhaps set it to switch on around 2°C / 36°F and off around 5°C / 41°F.

That should do exactly what you're describing without needing to find a specialised “battery warmer”.

Personally I'm leery of anything that would stay plugged in to the battery pack. If the thermostat fails it might cause damage.

Can you describe your larger system? How are you charging the battery pack? If it's solar with a controller, could it power a small 12V incandescent bulb directly?

Howdy, I think USB cables have a max 5 Amp limit and most not rated that high?  So charging USB .5 - 3 Amp max usually.  Like Douglas said “Leery”, I would be as well as cable failure is a fire.  Might be looking for a different system, like solar recharge buffering/dump which changes loads to secondary systems (like heaters) once charge reaches max.  While your charging heat is generated in any battery system, then dump to secondary heater.  If you have a central heated area for battery storage this increases efficiency of the entire system.  A life of integrated technology requires large structural change… I’ve decided to place it in a separate building not a central living space.  Cheers