Charging Batteries in Cold Weather
One of the biggest misconceptions is that batteries charge the same throughout the year. They simply don't! In warm weather (above 40 degrees), batteries are very easy to recharge. They can normally take as much charge that the vehicle charging system can provide. Even deeply discharged battery packs can be completely recharged in a few hours if the only issue is a discharged battery not defective batteries.
However, the colder it is outside, the less charge the battery pack wants to accept. When it is very cold, the electrolyte in a flooded cell battery becomes like jelly and the molecular action in the battery slows down. The battery is similar to a tube of toothpaste -- difficult to get out and almost impossible to put back in.
The operator may become fooled by the way the vehicle responds in cold weather. The voltmeter on the dash displays a correct charging range and the lights are bright so it is assumed that the batteries are charging as normal.
What is really happening is that the vehicle's alternator is at the correct voltage and is powering the vehicle loads, but because the batteries are cold, the charge acceptance of the batteries is very low, sometimes as low as 2 amps per hour. Driving times of up to 40 hours can be required to charge deeply discharged cold batteries.
While AGM batteries have up to 40% better recharge capacity across all temperature ranges they will still require more time in cold weather to recharge than driving laws allow.
Things to remember in cold weather operation:
* Discharged batteries can freeze in cold weather.
* Never try to jump-start a vehicle that has frozen batteries.
* Cold batteries will not accept a normal charge until the batteries reach an ideal temperature or extensive charging time is available.
* Cold batteries can take up to 30 hours to warm back up to room temperature.
* While jump-starts can get the vehicle started, many hours of charging may be required to recharge the battery pack. It might be a more prudent path to change batteries as normal vehicle operation cannot recharge the battery pack adequately during a normal workday.