Battery heating pad versus small charger?

[wopachop]

I have two flooded 6v batteries on a trailer tongue. Outside temps are around 30-50F. In the next couple years i plan to switch to lithium and move the batteries indoors to stable temps. For now i took a quick look at battery heating pads. Not the cheapest things and in a few months its going to be 90F outside and wont need them.

Instead of buying a 60watt heating pad, what if i hooked up my 60watt battery tender to the inverter powered by the same batteries? Do you think a 60watt charge and discharge would be enough to raise the temp of the batteries? Or will most of the heat production and heat loss happen at the inverter, making this idea useless?

The goal would be to warm the batteries a bit before putting a larger load on the inverter. I would definitely unhook the charger while not in use. Solar will charge the batteries during the day. More looking for a cheap and temporary way to warm up my 6v's until i switch to lithium and can move the batteries inside.

 

[time2roll]

60w is probably more than needed. Small 10w is $3 and maybe get a thermostat.

https://www.ebay.com/itm/313945724560

https://www.amazon.com/Temperature-Controller-Thermostat-Waterproof-Programmable/dp/B07H2ZDDF1

 

[wopachop]

The 10w heater looks to be the way to go. Hooked up 400w inverter and small charger. I realize now the charger does not have anyway to go through the battery. So its not a charge and a discharge. Only a discharge.

Using a smaller 0.75a output battery tender. The inverter is using 1.78amps and the battery tender is pushing 0.78a. So i think all that is happening is a 1amp draw on the battery.

For kicks im taking temp readings. The battery was at 39F when i hooked everything up. I moved the battery to a colder location. At this point im expecting the battery to be colder in 1 hour. The heat is probably going to the inverter? The little battery pad must be the better choice. I dont think using a charger to warm the battery is really a choice at all. Unless you had 2 terminals maybe? If you could enter the power on 1 side. Then draw from the other. Of course there would be loss in the inverter. But i was hoping to excite the battery somehow, using the battery itself. The battery heater pad sure makes it easy. Since the heat will excite the battery.