battery life

[Larryjb]

I know this topic seems to have been done to death, but.... here goes...

I plan to dry camp one night at the Columbia Ice Field. In the summer, temperatures can drop to 5°C (about 40°F), so we will want to use the furnace. Most lighting is LED. The only electrical loads I foresee is the furnace fan, roof vent fan, LED lighting for the evening, and the toilet.

I presume the biggest load will be the furnace fan, and roof vent fan. I may use the roof vent fan on low to keep fresh air circulating, and we may be using the LED lights for about 6 hours. On a full charge, should I be OK with this?

The one main issue I see is putting the fridge to 12V when travelling. I'm not sure if the battery will be on a net charge or drain with my Tahoe.

I may pick up a 2nd battery to either keep as a spare, or wire in parallel. I may just use it as a spare because I'm not sure about charging two different batteries of different ages.

[Larryjb]

I ran the furnace for about 3 hours on battery only. The roof vent fan was running on low.

I didn't measure the voltage at the beginning, but at the end of the three hours the battery voltage dropped down to 12.0V with the fans running. With no loads, the battery voltage went back to 12.6V, but I remember being taught to always measure battery voltage with at least some load.

Given this, I wouldn't trust this battery for overnight dry camping with a furnace. So I guess I have a revised question:

Should I be able to get a night or two running the furnace and roof vent fan, along with the LED lights on at times?

[fairweatherfisherman]

I always carry a charged up spare AGM battery in a battery box in our TV.

[tentcamper]

I assume you have a group 24 battery (about 60 AH, usable about 30 AH when fully charged) and that the TV has the charge line. Once you arrive at your camp site you will run the fridge on propane. I believe once you get to the campsite your battery will be between 12.4-12.5v. or about 70-80% charge. This will leave you about 20 to 25 AH of usable current

Not sure about the fan, I would try just opening the roof vents and some windows. At forty degrees and running the furnace for 12 hours at 68 degrees. You will use about 20 amps . I would bring a second battery or replace my current battery with a group 31 with 105 AH and about 50 usable AH. I would also bring some good jumper cables, just incase?

[Larryjb]

I looked at the battery today. It's Walmart's Everstart 27DC. I believe the rating on it was close to 100Ahrs. However, lots of people report that it fails to keep a charge after a year.

After charging it for 6 hrs, it has a voltage of 13.2V unloaded. I think I am supposed to measure the voltage unloaded. That means that after using the furnace for three hours I was down to 12.6V, so I still had a little reserve left, but not as much as I'd like.

[rmcmeeking]

A non-battery related suggestion. Set your thermostat pretty low, maybe 55-60, and have good sleeping bags. If you close the curtain between the wardrobe and bath it helps retain body heat in the sleeping area.
Haven't been there since '78, but you'll never forget it. Note the snow buggy and tourists in the pic bottom right. We did this trip with an Apache canvas pop-up, no heat, and survived.

[Larryjb]

Thanks rmcmeeking,

I am planning on the worst, needing heat overnight. I've told my wife we'll want sleeping bags, and then I'll assume I'll be the first up and get the furnace warming up the trailer for breakfast. I'm really looking forwards to this trip.

I should see if I can look up the Ahrs for the furnace fan and see if I am getting appropriate capacity from the battery. At first I assumed that I should measure the voltage under load, but that seems to be incorrect. However, I thought a fully charged battery was supposed to be around 12.6V. This one seemed to be at 13.2V after I removed the power chord. I did run the roof vent fan on low while measuring the voltage and still got what I thought would be a high measurement for voltage. I'll measure it again today after it's been sitting for a day.

[tentcamper]

I always check my battery without a load after a short rest. It gives me a better view of the charge left.

I'm thinking of getting the sam's club g31 battery rated at 105 amp hours. It's a duracell. I believe that battery plus has the same battery.

I would think your furnace will run at 40 degrees outside and set for 68 about 5 minutes every 15 to 20 minutes. It will draw about 6-7 amps per hour when running.

For what it is worth. If you were not depleting the g24 battery to run the fridge and the battery will hold a good charge. I would not have any concern with running the furnace one or two night for 10 hours. Some people talk about traveling a few hours without the fridge running.

Also, you will always hear stories about batteries only lasting a year. Most people do not maintain a battery over the winter. Many times they leave it hooked up with an active load and full discharging the battery. No battery will hold a good charge after being fully discharged for la long period.

[Casey Freswick]

If you have any real concern you might check out a no vent propane heater. Like old kerosine heaters these require no electric. I have not seen a thread about this type of heater, but I have read on-line that some boondockers have gone to this set up. Not sure if anyone with TM has hooked this up. I have not done it but am considering it.

[Bill]

Agree with Casey. The big names in no-vent catalytic propane heaters seem to be
o Olympian
o Mr. Heater Buddy
There are others, of course, but these seem to get the most attention in the RV world.

Bill