Killing your car battery is a rite of passage for any driver. Sooner or later you’re accidentally going to leave your headlights or cabin light on overnight. It’s just one of those things.
And with that rite of passage, invariably, comes another: Jump-starting a car. You connect the positive booster cable (the red clamps) to the positive terminals (usually marked with red or a “+’’ sign) first. Then you connect the negative cable (with the black clamps), first to the negative terminal (with a “ - ’’ sign) on the good car, then onto the dead battery’s negative terminal, or an unpainted part of the car’s grounded metal frame.
This much - I think - most drivers know, or learn very quickly. But what else do we know about our car batteries? What else should we know?
Case in point: A few weeks ago, my friend Maria got a new battery, and that very night left her cabin light on. “Did I damage it already?’’ she asked. Neither of us had a clue.
With winter soon upon us, there’s no better time to find out the answer. This week, a lesson in battery basics.
Are you damaging your battery every time you leave the lights on?
This is the question we all want to know. The answer? Not necessarily, but you have to be prudent, those interviewed said.
“If it’s just something that happens one or two times, no damage,’’ said Jeff Short, owner of Royal Battery in Malden, who’s been fixing batteries for decades. “You just need to jump the battery and run it for a certain amount of time. The car’s alternator will bring the charge back up.’’
The key words are “a certain amount of time.’’ If you don’t run your car long enough to bring the battery back to full strength - it could take 20 minutes, or more than a hour if it’s badly depleted - you could very well truncate the battery’s life.
John Paul, AAA of Southern New England’s “Car Doctor,’’ once told me that a battery can lose up to 10 percent of its life span every time it goes dead. Battery Council International, a national trade association, told me the damage would be much less, closer to 1 percent.
Either way, you’d be smart to take your car to a service center after getting it started and have the battery slowly recharged back to full strength over two to three hours, said Skip Mucci, who ran a Malden towing company for 15 years.
“The slower the charge, the better the battery is going to come back,’’ he said. “I used to tell all of my customers that.’’
Having a dead battery in the winter can be worse than in the summer, experts added.
For one thing, it takes longer to recharge in colder temperatures. But there’s also an added wrinkle in terms of the battery’s internal chemistry.
Batteries contain sulfuric acid and water in a specific ratio, Short said. When you leave your lights on, the acid loses its electric charge, throwing off the ratio and killing the battery.
“If you left your headlights on overnight, the acid would almost test to a water state,’’ Short said. “If you discharge the battery in the summer, no big deal. But if you discharge it in the winter, and it freezes, in a few days your battery will be a block of ice.’’
Will charging your phone or iPod when your vehicle is off deplete the battery?
Because the draw is so minimal, it shouldn’t, experts said. The only time you’ll have an issue is when something’s wrong - either you’ve got an electrical short in your car, or your phone charger isn’t working properly - and juice flows from the battery unchecked. When that happens (it’s called a “parasitic draw’’) you’ll probably need service.
Are you weakening your car’s battery by giving someone a jump-start?
The concern isn’t so much with the battery, Short said, but what a jump-start might do to the car’s electrical system. In particular, its onboard computer.
“There are cars being built today that if you jump-start them, you can ruin the whole computer system,’’ he said. “You have to refer to your owner’s manual for proper procedures on jump-starting, or giving a jump.’’
I posed this same question to the Battery Council. They said that most cars are designed to give and receive jump starts, with two notable exceptions.
“Do not attempt to jump-start a hybrid or electric vehicle . . . or use them to jump-start other vehicles,’’ the council warns. “They use a higher voltage battery, and it is a different chemistry: lithium ion.’’
If you’re concerned about jump-starting your car in conjunction with another vehicle, the safer option might be purchasing a portable starter, available for $50 to $100 at auto supply stores. But again, read up on your car first.
Does car size matter - i.e., should a Mini Cooper attempt to jump a Dodge Ram pickup, or vice versa?
“As long as your battery voltage is equal, you’re fine. And just about everything made today, with a few exceptions, is 12 volts,’’ said Short. “That doesn’t mean it’s always going to work. There are times when a battery is so dead it won’t accept a jump start. But there’s no formula to say when it will and won’t work. You just have to try.’’
Once you get a car with a dead battery started, you should probably run it for at least 20 minutes, experts said. Otherwise, the battery might not be charged enough to start it the next time.
How do you know whether the problem is actually with your car’s alternator, starter, or maybe a broken engine belt?
“Unless you say, ‘Oh, I left the dome light on,’ you don’t know,’’ said Short. “You have to have the proper equipment to test it.’’ That means a service call.
Even if your dashboard lights come on, you may still have a dead battery, he cautioned.
“You don’t need a lot of power to make the dashboard light up,’’ he said. “For your battery, that’s like lifting up a 5-pound dumbbell, whereas it’s like lifting a 500-pound dumbbell to get the starter going. So it could still be the battery.’’
More on batteries, next time.
Peter DeMarco lives in Somerville and can be reached at demarco@globe.com. He also updates a Facebook page, “WhotaughtYOUtodrive?’’ 
