[Shop-talk] AGM batteries: Protect from freezing?

[DAVID MASSEY]

It all depends on the level of charge.  A fully charged battery will freeze at about -70 deg F but a fully discharged battery will freeze at 32 deg F.  At 50% charge it will freeze at about -15 deg F.  An AGM battery is a bit lower.  Below is a curve from USBattery.com


Since you live in an area that can expect sub-zero (F) temperatures at some point over the winter leaving it out with a state of charge less than 60% is risky.
Dave 


 

    On Friday, November 14, 2025 at 02:39:12 AM CST, Philip Ethier <pethier7 at gmail.com> wrote:   

 

On Fri, Nov 14, 2025 at 1:34 AM Philip Ethier <pethier7 at gmail.com> wrote:

Absorbed Gas Mat batteries:

OOPS. Absorbent glass mat

If you leave a vehicle outside all winter in a cold climate without charging the AGM batteries, will they be ruined by the cold?
I know that regular lead-acid batteries can freeze up, but I don't know about AGM batteries.

-- 
Phil Ethier, West Side, Saint Paul Minnesota, USA2006 Gulf Stream Conquest Super C, 8.1, white2011 Cayman 2.9 PDK, white2021 Ford F-150 3500cc twin turbo, white1991 Caterham 1700 Super Sprint, not white
www.mnautox.com




-- 
Phil Ethier, West Side, Saint Paul Minnesota, USA2006 Gulf Stream Conquest Super C, 8.1, white2011 Cayman 2.9 PDK, white2021 Ford F-150 3500cc twin turbo, white1991 Caterham 1700 Super Sprint, not white
www.mnautox.com

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