On a recent family ski trip to Kirkwood, I pulled out my smartphone to take a video of my son on the slopes. The temperature was 25 degrees, however, and my phone died.
That situation reminded me of how cars can do the same thing in cold weather.
Calls from customers with dead batteries are common, but we receive more of them in the winter months. The second week of December, we received two such calls. The first customer’s battery was 4 years old and the other’s was just a year old. But both customers said they let their cars sit for extended periods of time and didn’t drive them much.
The combination of no use and short drives is a killer for batteries.
Batteries rely on an electrochemical reaction to work. When it is hot or warm out, this reaction works normally; it slows down in cold weather.
And in these cases, both cars were not driven for an entire month over the summer. The lack of use weakened the batteries, but they did not die. But within the last month, both cars were not driven for two weeks – and this time they wouldn’t start. Both cars had to be jump-started and then brought to the shop for new batteries.
The most commonly used battery in today’s cars are lead acid batteries, which slowly discharge over time. The loss rate for a lead acid battery is 2%-8% per month at 68 degrees. On top of that, modern cars slowly drain power when they aren’t being used. The electrical system needs to go to sleep, but it never really shuts down – it’s like when you put your computer to sleep.
When a modern car is shut off, it has an approximately 100-200 milliamp draw. After roughly 30 minutes, that drops to 0.05 milliamps – an acceptable draw that will not kill your car if it is used normally.
I always compare batteries to athletes. Athletes who exercise every day and eat well will stay strong and healthy; those who miss weeks of training will eventually lose their form.
Please remember that if you plan to let a car sit for a long time or only drive it short distances, buy a battery tender. The device will help keep the battery in shape when the car is not being driven.