I drained my battery using it to power a small electronic device for about an hour with the engine off. I called for roadside assistance. After they got it to start and run for a few minutes, they turned it off and did some tests. They said their tests indicated the battery had a bad cell and needed to be replaced. The car starts and runs fine now.

I took it to a big box retailer that does free test and install. Their quick hand held test said it tested good. They ran it again on a different machine that took over an hour to run and again said the battery is good.

Should I do additional testing or just keep driving and avoid draining it with my electronics?

  • I took my car to the dealer for an oil change. They did a bunch of inspections and testing so they could s̶e̶l̶l̶ ̶m̶e̶ ̶s̶t̶u̶f̶f̶ make sure my car was running optimally. They too said the battery was bad. I made a mental note to get it replaced soon and went on my way. Drove across the state of Florida, tooled around town for a couple of days and the car failed to start when it was time to go home. Got a jumpstart, drove home with no trouble, got a new battery. So, Triple letter was right after all and Sam's-Mart was wrong.
    – TecBrat
    Commented May 15, 2018 at 20:08

2 Answers 2


I would assume that the roadside assistance test is bad and that the battery is okay. They sell voltmeters that plug into the cigarette lighter plug. I would buy one if I were you (I already have a couple) and plug it in for a week or two and check that the battery voltage is okay. It should be around 14V with the engine running and about 12.7 or higher with the key turned on but the engine not running.


I would suggest that your battery is ok - the roadside testing after a very short charge is highly unlikely to give anything representing the true condition of the battery.

It appears after all the other tests that it is fine, use it normally.

What you should consider for your electronics is a second battery with a split-charge system. This means that you can run your electronics until the second battery is low and still be able to start the vehicle.

Places that do caravans tend to know about split charge systems and so do places that do winches. The bay of fleas is a possible source of relevant parts, but any competant auto-electrician can do this (a nice easy job...!!).

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