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Old 12-06-2010, 09:30 PM   #1
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Cold weather and batteries

A common question about wintertime motorhoming is how long will my batteries last under various conditions. Usually it's the heating of the motorhome which will draw down the batteries overnight.

What might be good to investigate and I think it is overlooked, is buy battery heaters.

The temperature most liked by a lead acid battery is 77 degrees.

Many batteries are sitting out in the sub freezing temperatures and their output will drop dramatically even if new.

There are several 12 volt powered heaters available.

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Old 12-07-2010, 11:49 AM   #2
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12 volt heaters such amp hours like you would not believe.

Of course running a 120 volt heater off an inverter... IS WORSE.

Home is where I park it!
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Old 12-07-2010, 12:29 PM   #3
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I was thinking of this

Originally Posted by wa8yxm View Post
12 volt heaters such amp hours like you would not believe.

Of course running a 120 volt heater off an inverter... IS WORSE.

I was thinking that a bunk warmer might do several batteries, sort of like the T36 which draws 6 amp at 12 volts.

You can find it here. It doesn't catch fire underneath you so it seems like a safe product. Maybe a little reflecting materials could help as well.

Electric Heated Mattress Pads - Bed Warmers by ElectroWarmth

120 volts models I didn't consider since I figured people are only concerned when they are not hooked up.

Just an idea.
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Old 12-08-2010, 02:49 AM   #4
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i have been using a 12v heated mattress pad from backwoods solar since 2007 with great results.
01 WINNEBAGO 35U W20.8.1L SW Wa, Hi. Good Sam, SKP. AMSOIL fluids. BANKS ecm program. SCAN GAUGE II w/ Ally temp. 2 LIFELINE GPL-6CT AGM Batts on their sides. TST tptts. K&N panel air filter. AERO mufflers. TAYLOR plug wires. ULTRA POWER track bar. KONI fsd shocks, toad '14 smart car
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Old 12-08-2010, 10:01 PM   #5
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Insulation, mass and heat

One could get some water heater wrap to insulate the batery box, this would reduce heat loss from the batteries.

Next, the batteries are very heavy, it takes a lot of time and temperature differential to actually drop the temperature, so insulation will slow it down.

Next is heat, depending on the use of the MH, one could route a water line from the engine heat into the area with the batteries, a single turn or 2 of copper line secured to the wall inside the insulation would add heat, a ball valve would shut it off durring summer, use a return line from the heating system and use a "T", if no "T" then depending on your system the dash control may be OK.

So while driving it warms the batteries up, then the isulation helps keep the heat in so it is not as bad.

Our coach has a duct from the heater into the chamber that has the water tank to keep it warm, you could also do this, find a duct close to the battery box from the heater that you will use, tap off and rout it into the insulated battery box.

Small 2 inch or so is all that should be needed, but you can determine this epending on your heat loss.

Good luck!

If AC is not available then battery power or mass will be needed, I think you best bet is insulation.
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Old 12-12-2010, 05:59 PM   #6
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Two layers of the household foam sheet (without aluminum backing) is R 4.4 and 75 watts will keep a box big enough for two batteries at about 70*F if I remember the calculations correctly. Battery heaters are typically designed to just go under the battery wihout insulation. good to calculate the power drain that would justify the use of power for heating vs. the loss of efficiency due to being cold. havent done that yet.

The ideal place for free heat would be the generator radiator. A couple gallons of hot water holds a huge amount of heat. Might insulate the compartment and put a small radiator in it and feed some gen coolant to it.
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Old 12-12-2010, 09:21 PM   #7
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Trip to wrecking yard...

Did not think about the generator water if it has it.

A heater core from the wercking yard would be good to supply the heat if you could find one cheap.

You also could get some copper tubing and make one with a simple coil that goes around the area of the batteries.

It needs to be at distance to avoid overheating of the batteries.

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