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)
You need to clean your battery terminals.
Agreed. Disconnect the battery cables. Using files, sandpaper, penknife, etc, clean the cables and battery posts.
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.
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.
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.
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.