Every January the phone rings with the same story: the truck started fine yesterday, it's minus thirty-eight this morning, and now it just clicks. The battery wasn't bad yesterday. It's just that cold changes the math.
What the cold does
A lead-acid battery is a chemical reaction, and chemical reactions slow down as they get colder. At minus eighteen a battery delivers roughly half the current it does at plus twenty-five. At the same time, the oil in the engine has thickened to something closer to honey, so the starter needs more current to turn it over. Half the supply, double the demand. A battery that was at 70 percent of its rated capacity in October simply doesn't have the margin.
Three things worth doing before freeze-up
- Get it load tested. Not a voltage check; a load test that measures cold-cranking amps against the rating on the label. We do it free with any fall service. If it's under about 75 percent of rated, replace it before winter, not after.
- Clean the terminals and check the grounds. A fuzzy white terminal or a corroded ground strap can drop enough voltage to make a good battery act like a dead one. Five minutes with a brush and some protectant.
- Plug it in. A block heater warms the coolant and the oil around it, which cuts the current the starter needs by a surprising amount. Below minus twenty, plug in for at least three or four hours before you start. A timer that kicks on at 3 am saves power and does the job.
When to plug in and when not to bother
Above about minus fifteen, a healthy battery and the right oil will start most engines without help. Below that, plug in. Below minus thirty, plug in and consider a battery blanket if the vehicle sits outside. If the block heater cord is more than a few years old, have it tested; cords fail more often than the heater element.
Buying a battery
Buy the cold-cranking amps, not the brand. Look for a rating at or above what the manufacturer specifies and a reasonably fresh date code (the sticker on top). A battery that has sat on a shelf for a year has already lost some of its life. We stock batteries rated for the prairies and install them with the terminals protected, and we'll recycle the old one.
