View Full Version : Amx losing battery power

05-24-2007, 04:36 PM
I have a 1970 amx with 390, and the battery will not keep its charge. I have a new battery and voltage regulator. I have also had the alternator checked out and it is working fine. I drove around yesterday for 23-30 minutes and when I went to start it up and hour later the battery was dead. Has anyone experienced this before? Thank you in advance.

05-24-2007, 05:51 PM
Is the ground wire tightened on the motor?

05-24-2007, 06:41 PM
Yes, I checked to make sure all the connections were clean and tight.

Big Bad AMX
05-25-2007, 11:39 AM
If it was fully charged before you drove it and you only drove for 30 minutes (without any accessories running) it should have enough left to start at least once. My first impression is to suspect the battery is weak or has a few dead cells, even though it's a new battery. Also what's the battery's CCA? And is it a wet cell, dry cell, or gel cell? I would have the battery tested under a full load.

Did you just have the alternator checked or was the system checked to see if it was charging at the battery? You really need to know if it's charging at the battery to narrow down the possibilities for trouble shooting.

And how old are the battery cables? Even though they look clean and tight I've seen cables corrode and break under the insulation, usually within an inch or so of the terminal. You may want to check that.

I have bought two new, but bad, voltage regulators in a row before. So do have it checked at the battery. Anymore I don't assume that just because it's new it's good.

After you get this problem sorted out you may want to look into a Battery Tender. It'll keep your battery peaked and in good shape when your car is sitting for an extended time (a month or more). They're a must for winter storage. You should be able to find one for $20-25.


05-26-2007, 12:43 AM
question-----using a voltmeter,what is the voltage at the battery post @ 1200 RPM? a FULLY charged battery should read about 12.4-12.6 volts.when running at high idle you should have between 13.8-14.2 volts IF the charging system is working.i've had motorola alternators put out only 13.4 but those were ones that i knew were on the weak side.also are you getting a large current draw when the engine is off?this could be a bad isolation diode or the diode plate is grounding out to the alternator casing.how was you alternator checked may i ask?

01-05-2008, 02:21 PM
I kind of have the same problem with my 73 Hornet (V8). The problem I have is that the battery is loosing its water after a few months of driving it. Last winter I put the car in its place in the garage and low and behold, the stupid battery goes dead. Not good considering that the garage is an unheated garage and we do get temps in the below zero readings at night. Anyway, I put a battery voltage meter on it and it shows that its charging at about 14 volts at 1500 RPM and about 13.1 (or so) at idle. What I did notice is that the water level is almost nil and I have to fill the water level back up with distilled water. What I cannot figure out is where is the water going??? This is the second battery that this has happened to and I find it somewhat aggravating in that it does this. There is no evidence that the battery is boiling it out (no residue on the battery itself or the bottom of the battery tray) but it got to be in that perhaps its vaporizing (although I have never seen this done before without leaving some kind of evidence in the engine bay area). The Hornet has a new voltage regulator, new cables and the such. The only thing that I haven't changed is the alternator and perhaps that is my problem. Anyone has any ideas????