battery causing alt overcharging?

[tyrantfour]

hey guys, this is going to be a long one cause its a long story. but for those not interested in every detail, scroll down to the last paragraph for a sumary.

I just bought a new (to me) 2007 focus Se with the 2.0 engine and automatic transmission. It has 27K ish miles and everything is very clean. Carfax reported this car to have had all the maitenance performed as necessary.

During the test drive, everything was great! However, the day after I brought this car home, Im talking less than 50 miles later, the turn signals quit working, the battery light and door ajar light came on. they went off and the signals started working again. later, i noticed that none of the cluster electronics were working. by the end of this trip the battery light would come on and stay on.

My boyfriend checked the voltage on the battery with engine running and was reading 15.25+ and noticed the battery was actually bubling acid from the caps. So, as he is a good mechanic, diagnosed it saying that the alternator is overcharging the battery causing the bubling and associated oddities. To confirm, we took it to advance auto to get an alt test. They tested it and showed 17+ volts unloaded, and 16+ loaded. The parasitic load was at a whopping 4.87 Amps! To confirm yet again, lol, we took it to autozone, and yes it was charging at 17+. They also noticed that the battery that was in the car was a 26R, wheras it called for a 96R.

The dealer said, the alt is fine because the car has only 27K miles. So i took it to his shop and they said the same thing that the battery somehow causes the alternator to overcharge the battery because the battery is bad???? WHAT? It seems they are mistaken...the batter is bad because the alt is overcharging, as evident by the boiling over of the bat acid.

They replaced the battery with a new lookin 96R. and that was it. So now ive driven 30 miles and havent had any problems yet. I took it to advance and had it retested and they said it was passing. No load at 13.8. Parasitic load was non-existent at 0.00 Amps.

Sorry for this long post but if anybody stuck with me i could use some oppinions. If an alt is overcharging the voltage regulator is shot. But replacing the battery does not fix a faulty vr? Right?

my boyfreind was skeptical of the fix and it seems he was right. today, after about 100 miles i started having all the same symptoms again. guagues, signals, and such not working. bat light came back on. so i took it to advance again and they said it was charging at 17.09 volts under load. by the time i got it home, the (new) battery was leaking acid profusely and smoking heavily. once it all settled down i noticed the battery was actually swollen pretty good.

well i called the dealer and they said blah blah blah bring it in on monday, they couldnt care enough about a paying customers precious time. so as it seems, the alternator is what caused the previous battery failure, and the failure of this new battery.

i highly doubt that they did not know about this issue before they sold me a 10K dollar car that needed 300 dollars worth of parts out of the gate. they dealer said he actually drove it all week before we bought it.

can a bad battery cause an alternator to overcharge? evidence suggests it can, but not in this case. and yet the question remains, if the alternator is indeed at fault, why did it take 100 miles to nearly detonate a new battery.

******************SUMMARY******************
bought a newish 27K mile car. 30ish miles later it started acting funy, cluster and signals not working, ended with battery light being on, everything works again. pop the hood and the battery is boiling over, have it tested, alt is charging at 17+ volts, notice bat too small. dealer says just a bad battery and replaces it with a new bat. have it tested, sitting comfortably at 13.9 volts. 100 miles of error free driving, the new batery is boiling over, expanding and smoking heavily, have it test, and its again charging at over 17+ volts. what makes an alternator to overcharge, stop with a new battery, only to begin overcharging again a short time later, to the point of turning a 12v battery into an IED? im baffled!

[inafogg]

sure a dead cell in a battery may/will never show a full charge

[Davescort97]

Replace the alternator. Voltage regulator is inside. It is the problem.

[Scrapper]

i got a buick skylark it's a 93 battery wont hold a charge and makes it over charge also i had a new yorker did same thing put new battery in and was good as new. he may be rite also.

[stv840]

I admit I only read your summary but I have some exsperiance with fords

There are probably two major problems the alt and battery is one but there is probably a electrical drain on the battery as well that's why throwing a battey in it solves the problem. ck this by pulling the positive wire on a known good battery and placeing a test light between the post and wire if it glows with the key out and the hood light disconected you have a drain in the electrical system narrow that down by pulling fuses.
The two electrical problems are masking each other you could test everything with a good old fasioned VAT two 15 min charge test would conferm the alt.