Battery wont hold charge?

[Guest Anonymous]

I just replaced the battery on my 76 2002 because the old one was shot. It was having a hard time starting( not enough power) i put the new one in and it started great. BUT after about a week, it started losing power again. I took the alternator out and it checked good so now i think it might be a ground or a relay. When i take the battery out and give it a full charge, everything is fine. when it starts to lose power and i take it out, it is down to 30-40% charge on the battery so im guessing it is not charging when i drive. Any ideas?

[Green2k2]

voltage regulator

these older cars have external voltage regulators (later designs moved the regulator internal to the alternator.)

It makes it an easy/cheap fix -opposed to changing the whole alternator itself.

[Guest Anonymous]

Where is the external volt. reg. located

[c.d.iesel]

voltage readings Please ? -

engine off _______ V ?

during cranking ______ V ?

at 3,000 RPM _________ V ?

at idle with headlight's on ______ V ?

[Green2k2]

Where is the external volt. reg. located

usually located on the fender-well next to the battery (stock location).

this link is just to show you what yours might look like (they may vary slightly) and I"m in no way suggesting you buy this from the link...was just looking for a clear pick and this is what I found in the first few minutes.

Your local autoparts store will have them cheap enough.

http://cgi.ebay.com/ebaymotors/BMW-1600-2002-2800-3-0-Alternator-Voltage-Regulator_W0QQitemZ260296408301QQcmdZViewItem#ebayphotohosting

[Mike Self]

perform a load test on it. I've seen (and owned) new batteries that had an internal defect that caused 'em to lose their charge and/or not accept one.

Also, check both battery ground straps (one to engine, one to body) to make sure they're clean, good & tight at both ends and not corroded or loose. Then check the brown ground wire that runs from the alternator case to the engine block. It can corrode under the terminals so that it still looks good but isn't. Without that ground wire, the alternator's ground path is very dodgy and will disrupt the charging circuit.

happy troubleshooting.

mike