Battery issue

Not sure if it's proper forum etiquette to start a thread on another problem while still trying to figure out the first problem (http://www.automotiveforums.com/vbulletin/showthread.php?t=920167), but here goes. :)

I'm having an issue with the battery on my 99 Taurus. The battery seems to have just enough power to start the car even though the voltage check is normal. With the engine off the voltage is 12.9 V, while running it's 13.75 volts. I had it checked at Advance Auto and their tester showed it was okay. While I was there I asked the guy to go ahead and check the starter. When I tried to start the car with his tester connected, the battery didn't have enough juice to start it. After he disconnected it, it cranked slowly but started. He was able to see that the starter drew normal voltage (I think he said 15.9 V). Then I drove to the grocery store. When I came out the car wouldn't start. I had to use the jump starter I have been carrying in my trunk since this started.

When I got home I hooked up my charger and set it to the 2-amp charge rate and left it on for about 9 hours. Then today when I was checking out my ignition coil pack (see other thread), I had to start the car several times. On the sixth or seventh time, the battery was too weak to start it. I let it sit for a few minutes and then was able to start the car. This happened again later. Battery was too weak to start the car, then after sitting for a few minutes it seemed to "build up" enough charge to start the car. By the way, the battery is only about 1 1/2 years old.

I don't find a question in this post, but suspect you want to know if it sounds like you properly narrowed the issue down to the battery. If so, I'd say I think you did. It sounds like the battery is weak. If you have a current meter (aka ammeter) you could measure the current draw on the battery when the car is sitting just to confirm the problem is not due to an excessive load on the battery. You'd want to leave the meter installed for about 2 minutes with all accessories and lights off to be sure the accessory delay relay and exit delay relays are open. Your current draw should be less than 100 mA.

If the current draw on the battery is not excessive, take the battery back to where you bought it, explain the checks you've performed, and they should pro-rate the battery for you. Often within the first 18 months they'll do free replacement (not pro-rated). They may want to load test the battery first, but it sounds like a good load tester should condemn the battery as well.

-Rod

Good point. I never really asked a question, did I? I guess I was wondering if a battery can be bad even though the voltage readings check out okay.

Yes, the battery's capacity can be low even if the surface charge/voltage appears good. A proper load test should indicate a capacity issue. It seems some of the modern electronic load testers don't really do a good job of indicating battery capacity though. I've had some of the parts store load testers say batteries were good even though they were not.

-Rod

Well, what I thought was a battery problem turned out to be the starter. Apparently the starter was "hanging up" and it was taking more battery power than normal, so it just seemed like the battery was weak. I put a new starter on tonight and it starts with no problems now.