AGM batteries and engine heat? Or heat tape?

P.S. and FWIW, I'm surprised that gel batteries are available anymore ... it seems like they would/should have sailed off into the sunsert by now!

Gelled electrolyte batteries serve one purpose well and all others horribly...

Temperature compensated float for emergency lighting. They are better than sealed flooded calcium calcium batteries because they can withstand more discharge cycles before destruction. But they cost more. And whoopee they an be mounted downside up. They also self-discharge a fraction of an AGM battery.

A good AGM battery will out-amp an equal amp hour rated flooded battery at zero degrees Fahrenheit. Tip: Do not use gelled electrolyte batteries for emergency lighting in a building situated at Prudhoe Bay, Alaska.

Both absorbed glass mat and gelled electrolyte batteries are referred to as VRB Valve Regulated Batteries.

i will note, i have done Very Few under 95 percent recharges
and the lowest SOC was down to 69 percent
they have not yet been reduced to 50 percent
they seem to really like getting back to full charge almost daily
in my case thats pretty easy to do, generator from 9am to lunch
then solar till 5PM then some more generator
but we are power hogs ( well i am ) , and 80 percent soc in the morning means we use 135amphrs, to be replaced

D'oh, MrWiz, you are right, and I am an idjit!

My current ice machine batteries ARE gel. I have always run AGM in the past and now I am old and forgetful. I've had these gels for a long time, and do not remember whether the AGM were different at low temps. It did not occur to me that they might be.

Glad to hear that yours are doing well!

:: embarrassed ::

are you sure those 'trouble some' batteries are AGM
they sound like GEL , even so they are 1/3 the AH capacity of these new batteries and you have (3) of them 405 Ahrs for the Van camper
and your largest load is you small MW, our MW pulls around 120amps on fully charged batteries around 104 amps in the morning

i have the same batteries, you do, i just spent all winter using them
this was a mild winter, coldest overnight around 30*, never had any problems
we used and electric blanket ALL night long, plus the fridge etc..
no power problems

yes chemical reaction response, for high output amps, is faster the warmer the chemicals involved, but i don't think you are going to have any problems with these, unless you are keeping them in a low charge state

these are high output server batteries, capable of supplying over 200amps per battery
rating is 500w max per CELL, thats 3000w max per battery,
of course thats only for 10 minutes, but thats a LOT of power

i think your worries about cool temp power output problems are unfounded in this particular situation

Thanks, everyone!

Best I can tell, my PD 9280 is not temperature compensated. But if I use it to charge 2 batteries @135aH, I am at around the 0.3C recommended for low temps. So that should be ok, yes?.

My concern is boondocking for, say, a week with nighttime temps in the 20s, without any driving.

Quoting for context, for those who don't like to go to the previous page:

I've been using AGM for about 20 years in my ice machine. My experience is that they are good (albeit a bit weaker) down to about 40 degrees, but once they get into the 30s they are nearly useless.

When I move camp to a place with warmer nights, it takes maybe 48 hours for my 45aH ice machine batteries to warm up, just from ambient temps. I'm concerned it may be a very long time for the bigger ones!

Naio,

I do not heat my batteries, but I do use temperature compensated charging.

Assuming your using a heat pad for the kitty and a blanket for yourself
Heating the batteries with battery power is just wasting the battery power
In really cold climates where heating the batteries or engine oil is required they use 120v shore power for that purpose
Not sure why you think you need to warm the batteries

If your planning ahead for a very cold North Minnesota winter
Go south, shore power, keep them fully charged

The Hot battery underhood, exposed to hot temperatures, and still enduring X amount of months or years has to have a few qualifiers.

First, Most of the time the underhood battery is already fully charged or very nearly so. it therefor cannot accept high amperages.

High amperages heat My AGM battery much faster than I ever expected, and especially so when on a hot ambient day. I've easily exceeded 107F in 85 F ambients with 40 amps available on a group 27AGM.

So if deeply discharged batteries were exposed to a high amp charging source, like a fast spinning alternator seeking mid 14v, then their temperature could rapidly climb if underhood, into the temperature zone where perhaps it is better no charging occurs.

Also this heating by higher amp charging can also be retained overnight on cold nights, as batteries are a huge thermal mass that take a long time to respond to ambient temps.

Not sure I'd use a heating pad for batteries, but perhaps try and retain the heat caused by charging/driving. Or just use less electricity overnight in cold temps, if possible.

Niao,

You can use a 120 volt heating pad. They are generally 50 watts. The bottom of the line from Walmart doesn't "time out".

I use one for my waste tanks and have an external mechanical thermostat on it.