# Car battery question. **URL:** \ **Category:** Factual Questions\ **Created:** [January 29, 2013, 2:29am UTC](https://boards.straightdope.com/t/car-battery-question/648679 "2013-01-29T02:29:33Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![Maserschmidt](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/maserschmidt/32/18829_2.png) [@Maserschmidt](https://boards.straightdope.com/u/Maserschmidt)\ **Post date:** [January 31, 2013, 12:05am UTC](https://boards.straightdope.com/t/car-battery-question/648679/21 "2013-01-31T00:05:38Z")
> [@ftg](#): > > I just replaced a battery yesterday. Almost 9 years old. The last battery I replaced in my other car (the infamous Mazda 323 from my recent other thread) was also 9 years old.\* > > I buy the “middle price” batteries and keep the terminals, etc. clean. > > I’d say having trouble with a battery 3 years old means there’s likely something else going on. There’s a lot to be said for pulling the battery connectors and giving everything a good cleaning. > > \ ***Mrs. FtG** ’s car, OTOH, just went thru a battery quite quickly. But that was more or less her fault. Well, Toyota’s too for making it too easy to bump a switch that leaves a nearly invisible light on. Last Sunday I replaced the battery in **mrs. Maser’s** Toyota after only 4 years. Which invisible light has she been leaving on again? 🙂 ---
**Author:** ![Rain\_Soaked](https://avatars.discourse-cdn.com/v4/letter/r/e19adc/32.png) [@Rain\_Soaked](https://boards.straightdope.com/u/Rain_Soaked)\ **Post date:** [January 31, 2013, 12:19am UTC](https://boards.straightdope.com/t/car-battery-question/648679/22 "2013-01-31T00:19:36Z")
> [@Maserschmidt](#): > > Last Sunday I replaced the battery in **mrs. Maser’s** Toyota after only 4 years. Which invisible light has she been leaving on again? 🙂 On our Toyota Camry, it is the rear seat reading lights that the kids can leave on unnoticed that will quickly drain a battery. All lights will stay on for about 30 seconds after you leave the car. The car will automatically turn off the headlights and other lights but will not turn off the reading lights. ---
**Author:** ![stui\_magpie](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/stui_magpie/32/11010_2.png) [@stui\_magpie](https://boards.straightdope.com/u/stui_magpie)\ **Post date:** [January 31, 2013, 12:54am UTC](https://boards.straightdope.com/t/car-battery-question/648679/23 "2013-01-31T00:54:44Z")
I replaced my car battery when it started to struggle, only to realise quickly that it was actually the Alternator that was the problem. I’m no mechanic but as I understand it all the car battery should do is provide the grunt to power the starter motor to actually turn the engine over. After that, while the car is running the alternator should be providing all the power needed to run the car, as well as topping up the battery. Of course, sitting in the car with the radio/lights/heater etc on when the motor isn’t running is a sure fire way to drain the battery. An easy way to test if it’s the battery or alternator is to do this. Start car. While car is running, disconnect battery. If car keeps running, battery is the problem. If car conks out it’s your alternator. BTW, I wouldn’t suggest doing it for long or in a new/expensive car. It can cause issues. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [January 31, 2013, 5:00am UTC](https://boards.straightdope.com/t/car-battery-question/648679/24 "2013-01-31T05:00:59Z")
> [@stui\_magpie](#): > > Start car. While car is running, disconnect battery. Do yourself a favor and _ **DO NOT** _ do this. Ever. At all. It’s possible to damage components like the alternator and the computer(s). This technique had some merit 50+ years ago on cars that had DC generators. On cars with alternators\* it can lead to expensive problems. \*There has been a trend over the last few years for car manufacturers to refer to alternators as “generators.” It’s fine to use that term, but be aware that all modern cars have alternators, which produce AC current which is rectified to DC, and are absolutely NOT DC generators such as were used decades ago. [Previous page](https://boards.straightdope.com/t/car-battery-question/648679.md?page=1)