Boon-docking on batteries

[Jester]

I have two quick questions. First will the battery in the camper be charged by the tow vehicle.
Second, how long does your battery last over night in cold weather with only the furnace on.?
We spent the night in Pennsylvania at Cracker Barrel with only the furnace on and the battery went from full charge to dead in one hour and ten minutes.
Btw 32 degrees That nite.

Is this normal?

[AZ Traveler]

Jester,

If all is working properly your truck will recharge your batteries while driving but at a slow rate.

The heater blower motor is a power hog so if you have a single small battery and the heater was running constantly it won't last long. If you are going to boondock a battery bank of 2 or 4 golf cart batteries gives you a lot more reserve. A battery monitor system is low cost and will give you a much better indication of your battery bank state than the simply lights.

[Creeker]

I've measured the charging amps from my last two trucks into several different battery banks over the years. I've never seen more than 8 amps no matter the state of charge of the batteries.

One group 24 size 12 volt marine battery is simply inadequate for dry camping in these campers. Lots of other small draws on that single little battery other than the furnace.

[DQDick]

As stated above there are many draws on the battery you can't control. All the electronics have 12v contol boards, even the frig on propane draws some 12v. Stuff like the propane detector also draw. When we boondocked we had six golf cart batteries, now that we don't we still have two batteries just for normal usage.

[twindman]

My first montana had one 12V battery. I was a newby and camped in the mountains with no power. I sat inside reading with lights on most of the afternoon and turned on the furnace around 7 pm, I think. The outside temp was probably 60 around 6 pm and got down to around 35-40 I think. By around 5 AM my battery died.
I had an inverter to power my CPAP and the inverter started chirping about low battery power. So I got up and put on pants and went outside and hooked up the truck and ran it for 30 minutes or longer. I got the battery charged enough to finish sleeping with my CPAP.
After that I did calculations. I think the furnace uses 9-10 amps when running. It seemed to run 3/4 of the time with the temps we had so that means it used around 7 AH from 6 pm to 5 AM -- 77 AH. Which, I think, is close to what a single 12V battery has.

[McRod]

Originally Posted by Jester

I have two quick questions. First will the battery in the camper be charged by the tow vehicle.
Second, how long does your battery last over night in cold weather with only the furnace on.?
We spent the night in Pennsylvania at Cracker Barrel with only the furnace on and the battery went from full charge to dead in one hour and ten minutes.
Btw 32 degrees That nite.

Is this normal?

1. Yes, your RV battery can be charged by your TV. It's the most inefficient way to charge them.

2. Depends on your battery setup. The furnace uses ~10AH. You will also have other parasitic power draws maybe another 5 AH. Who knows what else you had on or plugged in (phone chargers?)

If you have a 100 AH battery, it will last only <3 hours under those conditions.

[twindman]

Doesn't seem like your math is accurate. 10 +5 = 15. 100/15 = 6 hours. Perhaps you assume only discharging to half power?
Regardless, I ran my furnace overnight from around 8 PM until morning and still had power. I have 2 6V golf cart batteries, so I guess that is different. Back when I had 1 12V battery I ran from 7 pm to 5 AM and was about drained. I was in the mountains where temps were probably 60 degrees around 7 pm and 35-45 at 5 AM.

[Jester]

Thank you all for your answers. I need to make a couple of changes.
If I may add one more question?
If I leave the Montana plugged into my truck will the furnace have the single battery in the camper plus the two HD batteries in my truck to run the furnace and all the little parasites?
Thanks again.

[R.S.O'Donnell]

If you can swing even one Battle Born you'll save yourself a lot of headaches. I don't know which rig you've got but you might have a Lithium switch on your power center (our 3121 does). If so it would be a direct drop in.

We had two Battle Born's in our class C and could easily make it through the night and that includes a 12V dual compressor refrigerator/freezer, fans, furnace lights TV.

Never really knew we had "battery anxiety" until we didn't.

https://www.youtube.com/watch?v=WsVivNhfpjk

[mlh]

You need to add some capacity, either more batteries or a generator. I would suggest a simple inverter generator. They are quiet, easy on gas and fairly inexpensive. Harbor Freight makes 2000 watt for $499 or cheaper. You can find others even cheaper and much more expensive.
Lynwood

[McRod]

Originally Posted by twindman

Doesn't seem like your math is accurate. 10 +5 = 15. 100/15 = 6 hours. Perhaps you assume only discharging to half power?
Regardless, I ran my furnace overnight from around 8 PM until morning and still had power. I have 2 6V golf cart batteries, so I guess that is different. Back when I had 1 12V battery I ran from 7 pm to 5 AM and was about drained. I was in the mountains where temps were probably 60 degrees around 7 pm and 35-45 at 5 AM.

That's exactly right. You shouldn't discharge SLA batteries past 50%.

My 6v batteries are 225 AH. So yeah they will last longer.

[McRod]

Originally Posted by Jester

Thank you all for your answers. I need to make a couple of changes.
If I may add one more question?
If I leave the Montana plugged into my truck will the furnace have the single battery in the camper plus the two HD batteries in my truck to run the furnace and all the little parasites?
Thanks again.

No. They are not wired like that.

[H. John Kohl]

Originally Posted by Jester

I have two quick questions. First will the battery in the camper be charged by the tow vehicle.
Second, how long does your battery last over night in cold weather with only the furnace on.?
We spent the night in Pennsylvania at Cracker Barrel with only the furnace on and the battery went from full charge to dead in one hour and ten minutes.
Btw 32 degrees That nite.

Is this normal?

First question what model Montana do you have. Main reason is to determine if you have an RV refrigerator or Residential refrigerator.

[katdon]

No. It doesn't work that way. You don't want your truck batteries to go flat.

[Mocron]

I guess there is supposed to be some protection built in to certain 5vrs to prevent the rv from being able to drain your tv batteries. My first Montana didn't have that protection and we suffered the consequences. Shortly thereafter we had a relay installed to remedy that. No more issues. (Sorry, but I don't know any more about the relay.)

[Mikelff]

Originally Posted by Jester

I have two quick questions. First will the battery in the camper be charged by the tow vehicle.
Second, how long does your battery last over night in cold weather with only the furnace on.?
We spent the night in Pennsylvania at Cracker Barrel with only the furnace on and the battery went from full charge to dead in one hour and ten minutes.
Btw 32 degrees That nite.

Is this normal?

Yes. You need :
An inverter generator, and/or more amp hours. Depending on how much boon docking you will be doing, you will want a lithium battery, or two 6 v batteries for more amp hours. You will still probably want an inverter generator. If you typically hook up to shore power a 100 amp hour lead acid battery should take care of you. If you run a 100 amp lead acid deep cycle to 0, dead, it’s toast. You need a new battery. You can only run them down to about 50% (50 amp hours). Do your research first before you buy anything and then determine your power needs based on the type of camping you intend to be doing. Lithium are up front expensive but last for years, and are light weight. Most have a 20% auto shut off and charge faster. 6v will give you a lot more amp hours, but are heavy and don't last as many years as lithium. I get by fine with a 100 amp hour lead acid because I'm always on shore power. Still strongly looking at an inverter generator for back up power and the rare chance I’m having to boondock for some reason. Has happened, but in mild weather not requiring A/C or heat. Research!

[DebNJim B]

I had a single Marine type battery from the dealer rated at 70AH. Residential fridge would kill it overnight. Needed to go larger and was looking at 2-6v set up when I found this battery.



We don't boon dock but sometimes overnight at a rest area or truck stop w/o shore power. This is 200 AH equivalent to two 6v batts. and nearly as heavy (130lbs). Had to use a portable engine hoist to get it in the compartment. Since it is a sealed AGM battery I didn't need the bulky vented battery box and gained much storage space in the forward compartment. My TV has a huge alternator and will charge it up just fine in between stops. I do carry a gen just in case we stay longer. I have only had it for two months but so far I am very pleased with the set up.

[Jester]

I have two such batteries now. They’re not as heavy as ur alone but together they add up to 130lbs. I don’t think I’ve ever ran them dead but who know, maybe next time.

[McRod]

Originally Posted by DebNJim B

I had a single Marine type battery from the dealer rated at 70AH. Residential fridge would kill it overnight. Needed to go larger and was looking at 2-6v set up when I found this battery.

Attachment 7777

We don't boon dock but sometimes overnight at a rest area or truck stop w/o shore power. This is 200 AH equivalent to two 6v batts. and nearly as heavy (130lbs). Had to use a portable engine hoist to get it in the compartment. Since it is a sealed AGM battery I didn't need the bulky vented battery box and gained much storage space in the forward compartment. My TV has a huge alternator and will charge it up just fine in between stops. I do carry a gen just in case we stay longer. I have only had it for two months but so far I am very pleased with the set up.

170 ah , 12v LIFEPO4, from bigbattery.com is now $899. I would offer that as a reasonable alternative to the Renogy AGM above. Gain 70 AH and save 100 lbs with probably 2x lifespan at an added cost of $500.


https://bigbattery.com/product/12v-lifepo4-power-block/

[R.S.O'Donnell]

Originally Posted by DebNJim B

I had a single Marine type battery from the dealer rated at 70AH. Residential fridge would kill it overnight. Needed to go larger and was looking at 2-6v set up when I found this battery.

Attachment 7777

We don't boon dock but sometimes overnight at a rest area or truck stop w/o shore power. This is 200 AH equivalent to two 6v batts. and nearly as heavy (130lbs). Had to use a portable engine hoist to get it in the compartment. Since it is a sealed AGM battery I didn't need the bulky vented battery box and gained much storage space in the forward compartment. My TV has a huge alternator and will charge it up just fine in between stops. I do carry a gen just in case we stay longer. I have only had it for two months but so far I am very pleased with the set up.

That's a very clean setup. I absolutely hate the box with the vent tube we have now. I finally got up enough courage up to try an overnight on them.

We were in the middle of nowhere so I could run the generator as long as i wanted. I kept it running until about 10:00 then shut everything down. By morning the batteries were right at 50%. So glad I didn't try all night as I'm sure they would have been stone dead.