Battery Question

pianotuna wrote:
adamis,

Starting with the RV at -30 in storage, how do you plan on heating the batteries up? You can't draw much current from them, so you can't run the furnace. It is a fail. You could run a generator, but DAMHIK that may not work too well. Shore power would work running an electric heater.

There is a good solution which doesn't involve Li, which is cheaper unless you wish to "roll your own" Li.

I am curious, is this your personal situation or a realistic hypothetical based on where you live. Being from California, I'm a fair weather guy so your needs and view point are clearly going to be different. If the camper is in storage, is it stored in a location where you have no power at all?

Our cold weather is probably laughable by your standards. The one time we did camp in some colder weather it was probably in the high 20s. Now ordinarily the wife and I would just put some extra blankets on the bed and turn off the heater for the night. However on this trip, we had our seven month old twin girls along so it was necessary to keep the camper warm for their sake because we couldn't put blankets on them.

This was about the 4th night of camping for us where we were running the furnace to keep things warm for the girls. The previous three nights was lower altitude so we still had some juice in the battery as it didn't cycle as much. We were also running two bottle warmers that pull about 600w for ~5 minutes several times a day. If I had thought about it I would have run the generator for the bottle warmers so we didn't tax our battery so much.

The 4th night was the coldest by far and the furnace ran off and on all night. Thankfully it made it to right about 6am in the morning before the battery died completely. At this point it was getting really cold in the camper, too cold for the girls. It being early I was hesitant to start the truck and disturb others.

My truck does have a DC to DC charger to pull power from the truck when it is running but because it pulls directly from the battery via a larger cable (not the accessory line on the truck), I have a switch inside the camper that disables all of this unless I absolutely need it and know I will be running the truck. I was able to flip the switch and pull power from the truck batteries long enough to run the furnace for about 30 minutes to warm the camper back up. At this point I was worried the truck might not start but thankfully, she started right up. I then ran the truck a while so I could continue to run the furnace and keep the camper warm.

So a couple things I learned from this. First, I didn't realize the battery wouldn't charge when cold (BMS) so even while running the truck, the DC to DC wasn't putting anything but a trickle into the battery. I realized this much later when it dawned on me the cold weather limits for charging. The second thing I learned is that if I did this type of camping more often, I would get at least one more 100AH battery along with another 200w of solar (for 400w total) to make sure those batteries stayed topped up. Finally, the fact that I had a LiFePo4 battery allowed me to run it down to zero without fear of damage to it. With AGMs, I could have also run them down to zero but there would have been lasting impacts.