Here are the facts:

1) The battery in my 85 300D has sounded weak when cranking since I pulled the car from winter storage in the garage after March. I charged it up though and the car starts right away every day. I figured driving would top off the charge if I had not charged it fully with the charger.

2) Yesterday was the first hot day when I had the A/C on and also had it out for an extensive drive into the city, about 12 miles on the highway. Not that far but more than my usual commute of 4 miles one way. I was going across the city at rush hour and was on a long downhill stretch. The traffic was inching along and I had a way to go downhill, so to conserve fuel, I turned the car off and coasted in neutral. When I got near the bottom of the hill and saw that I might make the next light, I tried to start it back up but the battery was near dead. Yikes!! Luckily there was a gas station on the right and I was able to drift right into a space. I called a friend, got a jump start, it started right up and I drove home without making any more stops. I did not use the A/C. When I got home I turned the car off and tried to start it again. No problem. It started up.

3) I tested the battery with a hydrometer to see if I had a bad cell. The readings were 1220, 1190, 1215, 1200, 1200, 1200. I tested the voltage after a short charge and it read about 12.70 V.

4) The car started up this morning, it started after work, and when I got home I did another reading. 12.57 V with the car off. I started the car up and did another reading with the engine revved and got 13.93 V

The reading of 13.93 V with the engine revved tells me that the alternator is OK, correct?

Did having the A/C on push the battery over the tipping point and drain it? Is it just not taking a good charge anymore and the extra load was too much for it? I cannot see a date on the battery but from what I can tell from the PO records, it was installed in July of 2001. Six years on a battery in my mind is a good long life.

Thanks for any input. I am planning on picking up a good Interstate battery tomorrow.

Richard

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