How long will batteries last?

[owenandkathy]

I have 2 6v deep cycle batteries wired in series. If they are fully charged, will they last for four days without shore power? We will only be using the lights and starting the propane fridge. Also 12v ceiling fan and heater. I don't have a generator yet. If it does run low, can i plug in a battery charger into my 2021 Expedition's 120 outlet? or will that drain the vehicle? Thanks in advance

[bsmith0404]

You should have roughly 200 Amp hours available. The biggest draw will be the furnace so how many hours you use that will determine how long they will last. Saying if they’ll last 4 days or not is impossible. It all comes down to how much you use. Running the furnace a couple hours at night vs running the furnace all night makes a big difference. Have I gotten 4 days out of batteries before? Yes, I’ve also run them down after 2 days.

[Canonman]

In my experience with a pair of 6 volt batteries, you'd need to be very frugal with your power use with no means to recharge. Maybe an extra blanket instead of the heater. Sitting outside in the shade as opposed to running the fan. If your trailer is equipped with LED lighting, great. They use very little power. Save your battery power for the fridge, water pump, lights when needed and you should get by OK.
I'd also suggest looking into a solar kit with the generator for backup. A lot less noise and fuss plus the prices have gone down as the technology has become more efficient and also more popular.

[chuckster57]

If you can determine the amp draw of the appliances/lights you plan on using you can make a decent estimate.

[sierraman68]

First remember that you shouldn't discharge the lead acid batteries more than 50% or they can be severely damaged. For example, if you have 200 AMPS from the two batteries that means that you really will only have 100 AMPS available.

I recently installed a Victron SmartShunt and was able to map out my 12V power consumption for each 12V device/circuit in my 25RES. With my rig disconnected from shore power and with nothing on I first determined the parasitic (background) draw. Then I turned on an individual device such as a fan, light, pump, or refrigerator, etc. and noted the amp draw of each item or circuit. This info was then stored in a spreadsheet for easy referral. Knowing the AMP draw for each device or circuit provides me a much better understanding of my power use and where I can best conserve if I need to. All this info was very easy to obtain with the Victron SmartShunt.