Car won't start after sitting for 3 weeks

Maintenance/Repairs
1

Netizens,

My 1990 Honda Prelude with the 2005 Sears Diehard Gold battery wouldn’t start after sitting for 3 weeks. Jumping it got it going right away. My ammeter shows that at idle, the alternator is supplying 7 amps of current to the battery so I don’t think I have an alternator problem. But I drove the car for a few miles after jumpstarting it. After letting it sit for a couple of hours it wouldn’t start again.



Is my battery dying, or do I need to buy a charger to keep it juiced up if it sits for a few weeks? (the clock and radio draw a couple dozen mA continuously)



Thanks.

2

You need to clean your battery terminals.

3

Agreed. Disconnect the battery cables. Using files, sandpaper, penknife, etc, clean the cables and battery posts.

4

What was the voltage at the battery with the engine running? 7 amps is only 84 watts, not very much; that won’t even cover the headlamps.

5

I suggest having the battery and the charging system tested. Many auto parts stores will do this free.

If you need to leave the car sitting for weeks at a time, consider a Battery Tender, which will keep the battery charged without overcharging it.

6

Thanks for the replies. I’m going to clean the terminals, although I don’t think that’s it- but you never known. For two reasons: 1. They look clean (I know, it’s the corrosion inside that counts… but they’re not corroded like in days of yore), 2. I messed with the cables and there’s been no change in behavior (in the past when I screwed around with cables, and they were the problem, something always changed). By the way, I measured current at the battery… the 7 amps was only the flowage into the battery itself. The alternator was still supplying current to the rest of the car, too. How much? I don’t know… I didn’t measure the rest of the car. But 84 watts being pumped into the battery sounds like a goodly amount of juice, and doing it at idle sounds like there’s plenty of the electrons to go around. If the battery was healthy I don’t think I’d want that much being pumped into it on a continuous basis. I’m wondering how the charging system could be at fault.

The battery tender is an excellent idea.
-the Pupp

7

It isn’t a good thing to let the alternator charge up a drained battery since it puts a lot of demand on it. If you have a battery charger I recommend you use it to charge it up and then have the charging system checked out along with a load test on the battery. I would also have the shop check for a parasitic current drain while the car is parked. You may have a problem there.