AGM Battery: Does it need a battery heater during winter months?
 

I recently installed a new AGM battery; I keep it on the charger on the weekends. So far, everything looks great! It has been very cold here this winter and I wonder if I should get a battery heater for it?

How cold and for how long?

It is about seventeen degrees tonight in an unheated garage. So far keeping it on the battery charger seems to be working.....

Unless the extra power of a warm battery is needed I wouldn't put a heater on it.

Are AGM batteries immune to cold?

Lead acid batteries, of which AGM is a variety, can have electrolyte freeze when their state of charge drops too low. A fully charged lead acid battery will require extremely cold temperatures (I want to say -65 or colder) to freeze, while a fully depleted battery may freeze around 30F.

AGM still has the liquid electrolyte, still has the acid, its just absorbed in a matt. That doesnt change the freezing point. The good news is that AGM tend to self-discharge less...

If youre keeping it on a charger, youre well ahead of the game. The small amount of dissipated energy in a float charge can create some heat, and it keeps the electrolyte in a concentration that is freeze resistant.

Most modern 'smart' chargers perform temperature compensation. Which charger are you using?

I am using a CTEK multi 7002 12 volt battery charger. It has a setting for AGM and seems to be working well.

The vendor's literature states "The MULTI US 7002 is certified for use between -4°F and +122°F" with no mention of any heating requirements. Your 17 F falls well within the specified range.

I also purchased the 7002 to use on my AGM. So far I think it is a great product.

Personally I wouldn't connect the charger more than once a week in weather above zero fahrenheit. But that is my thinking, not based on anything I've read so far.

I believe the battery will be more than adequate to handle the normal starting load if the glow plugs are working properly. I prefer to use the block heater that was installed either by the dealer or the factory. It costs about 5 cents an hour ( ten cents per kilowatt ) and in 15 degree weather two hours is typically the time I use the heater before attempting to start the car.

If the charger does not switch to ' maintain ' mode there is a chance the battery can be damaged ' from what I've read '.

For a battery that has too little to start automatically charging, I will set the 7002 to the setting ( SUPPLY ), that supplies a constant voltage. After a few hours I'll either select the ( NORMAL ) or the ' snowflake ' setting again for an AGM battery.

After the battery is charged and the 7002 switches to maintain mode. I will then do a reconditioning cycle by selecting the ( RECOND ) cycle.

This website link goes to the manual for the CTEK 7002:

https://smartercharger.com/products/ctek-multi-us-7002

It describes the 7002, has a video on how the charging cycle works, and a link to look at the manual or download a copy.

I had a 12 volt battery blow up once when removing jumper cables. Luckily I was wearing glasses and had a shower close at hand. So I try to be pretty careful to not ignite any hydrogen buildup.

Also I would not do the RECOND cycle with both battery cables connected. It pulses at close to 16 volts.

Yes, I always wear full coverage protective goggles when connecting or disconnecting battery cables. I need to start wearing chemical resistant gloves as well.

I have two E320 Bluetec diesel cars. They start easily at -20F without a battery charger or battery heater

Many of us could say that.

Doesn’t mean much. Batteries still self discharge. Cars naturally have a parasitic draw. Kinetics of batteries are still slower in the cold.