12v lead acid battery heater

[LeftieBiker]

How many AH /HR does it consume, roughly? I assume it cycles on and off after reaching the set temp. I know a guy who has to walk 5 blocks evening and morning, so he can plug in a trickle charger. Small car with small aluminum engine.

[ripple4]

The zero start 2800055 that I have here is 120v A/C and 50w, so that's like .4amps. I don't think its thermostatically controlled, so it just heats until the battery reaches equilibrium temperature, 50W in = 50w out. I have a mechanical timer that turns on 90 minutes before i leave in the morning, but it could be pluged in all night too, 10 hours would cost $.07 at my power rate, 90 minutes is a single penny. maybe other brands and models have different power/control mechanisms, or one could be added like that cold temperature power cube sold in home improvment stores. I see this for only mornings/days that are in the single digits and negative F temps. Above 30F, the battery should not have a temperature related loss of power.

[LeafTaxi]

I'd like to learn more about this subject, and it may well be the case that the posts i see on this forum with the always be trickle/float charging comments may still be valid for normal temperatures. but there seems to be a warning against charging a lead acid battery that is very cold.

To the best of my knowledge, the warning against charging cold batteries is because a very discharged, very cold battery could have become frozen solid; and fast-charging it (especially trying to jump-start it) may cause it to explode.

I doubt that attempting to trickle-charge a frozen battery at 20 watts would be enough to cause an explosion (though a frozen battery would fail to charge). Regardless, if you know that the battery is not frozen, then I don't think you need to worry about damage from trickle-charging.

The act of trickle-charging a battery also creates some heat. So my method to heat the battery up has always been to hook-up a trickle charger on very cold nights. I use a BatteryMinder Jr. these days: while the battery is charging, it is warming-up; and once charged, when the charger is doing its "desulfation" thing, that should add a bit of heat also.

Insulating the battery would also minimize heat losses, so would be valuable with, or without a heat source.

[BrockWI]

The battery warmers I have used about 50w also do have a high temp cut out, but when it's cold enough to plug them in it will never get that warm. For the heck of it I did try it in summer at 85 and it did cycle on and off, but below freezing I don't think it would ever get that warm.

I also would use a trickle charger, it adds a few watts of heat and keeps the battery topped off, two benefits in one. Granted it won't warm as much as a warmer, but the Leaf doesn't need to crank an engine over to "start".