People tell me their cart "lost power over the winter" and assume something broke. Usually nothing broke. Cold just does specific, predictable things to a battery, and it is worth understanding because two of them are recoverable and one is not.
Capacity drops, and comes back
A battery works by a chemical reaction, and chemistry slows down when it gets cold. At freezing you might see a lead acid pack deliver noticeably less than it would on a summer afternoon. Down near zero it is worse.
The important part: this is temporary. Warm the pack back up and the capacity comes back. Your cart is not damaged, it is just cold. So a cart that feels gutless on a January morning and fine again in April was never actually broken.
Charging in the cold is slower and less complete
The same slowed chemistry means a cold pack accepts charge more slowly, and a charger may call it done before it really is. Do that repeatedly and the pack drifts down over the winter without anybody noticing.
This is the argument for charging somewhere above freezing if you have the option, and for the monthly charger reset if you do not.
Freezing is the one that actually kills
Here is the part that matters most, and it surprises people.
A fully charged lead acid battery is mostly sulfuric acid solution, and that does not freeze until about 92 below. A discharged one is much closer to plain water, and it freezes near 32 degrees. In between, at around 40 percent charge, it freezes at roughly 16 degrees.
Now put Flathead numbers next to those. The coldest Kalispell has ever been is 38 below, back in 1950. Our average January low is just under 15 degrees.
So the charged pack has 54 degrees of margin against the worst night in recorded local history, and the half flat one is already below its freezing point on an average January night. Not a cold snap. An average night.
A full battery in an unheated shed is fine. A flat battery in the same shed can freeze solid, and when water freezes it expands. That cracks plates, and sometimes the case. That damage does not come back in the spring.
This is why "leave it charged" is the single most important piece of winter advice. Not because charge is precious, but because a charged battery cannot freeze.
Lithium is better but not immune
A lithium pack holds voltage under load far better in the cold, so the cart feels normal for longer. It also does not lose water and cannot freeze the way lead acid does.
What lithium will do is refuse to charge below freezing. A decent battery management system blocks it, on purpose, because charging a cold lithium cell plates the lithium and permanently damages it. If your lithium cart will not take a charge in an unheated garage in January, the BMS is protecting your investment, not failing.
What to actually do
Charge it fully before it sits. Reset the charger about once a month through the winter, or keep the pack somewhere above freezing. If you have lithium, do not try to charge it in a freezing garage.
That is most of it. Call me if you want a pack tested before the cold sets in properly. 406.270.9346.