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TR4/4A TR4--Diagnosing a Bad Battery

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KVH

KVH

Obi Wan
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I thought I knew a little about TRs, but I guess not so much.

My car wouldn't turn over on the ignition key, so I put the car on a charger and then checked each battery cell with a Specific Gravity tester. All looked great. The lights, radio, turn signals and all else also worked.

So I then used a hand-held MultiTester and saw 12.7 Volts.

I figured it had to be something else, so I checked the ignition wires, ammeter gauge, etc. No luck.

So I took a risk and just bought a new battery. Car started right up.

Short of a three hour Load Test at PepBoys, how was I supposed to narrow it to the battery if the charger, Specific Gravity and MultiTester all checked fine?

(the two screw driver spark test?)
 
At some point, you just don't have enough tools. A load tester is the right tool (HF has a cheap one for under $20) in this case, but I don't have one either. The things I would look at are :

1) Battery voltage with starter engaged. Under normal circumstances, with a good, charged battery, it shouldn't drop below 10v while cranking. Of course it might be that the starter is drawing too much current (sucking the voltage down lower); but you can get an idea of that by feeling along the battery cables. If the starter is drawing too much current, the cables will be fairly uniformly hot. But if the battery is the culprit, the cables stay cool.

2) How well does the battery carry the headlights. Should be almost no drop at the battery posts with just headlights on, at least 12.5 with a freshly charged battery.

3) After you've run the battery down significantly, how long does it take the charger to bring it back up ? For a 10 amp charger, it should take quite some time to pull the voltage back up ... if it comes up in minutes, the battery is likely bad.

BTW, the test at Pep Boys isn't always certain either. I had a battery once that I knew was going bad (car kept cranking slower and slower every time) but their machine said it was good. Eventually wouldn't turn the engine at all, so I took it back a third time and their machine said only "needs charged". Since it had just been on the charger for some 8 hours, I dared them to charge it and retest, which they did. Charger said it was charged, tester said "needs charged". They finally replaced the battery under warranty, but insisted on giving me a smaller battery than the one I had before ... last time I will EVER buy a battery at Pep Boys!
 
TR3driver said:
They finally replaced the battery under warranty, but insisted on giving me a smaller battery than the one I had before ... last time I will EVER buy a battery at Pep Boys!
Click to expand...

I've had good success getting batteries at Costco... just put a Costco battery in my folk's Acura this evening. 100 month battery, first 36 months free replacement, for $47. Their batteries are made by Johnson Controls, highly rated in some test I saw somewhere.....
 
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