Thread: Battery not charging - alternator test Ok.

Hey guys,

Having a little issue with my battery not charging.

Thought the alternator must be bad, so fitted another one. Before fitting it I had it tested and refurbished with new bearings etc.

However, the battery is still not charging. What could be the problem?

Could be a bad battery as well, but I doubt it. Either there's an issue with the alty, or your wiring between the two is bad. Could also be a fuse that's blown somewhere along the line, or a bad connection to your instrument cluster.

The Big Question that will help immensely:
Does the car run off the alternator, or does it draw from the battery until the car eventually dies?

Bought a new battery as well. After it now died on me I charged up the battery using a charger and ran it in the car. It just slowly drains and after a few minutes the battery will be at 10v and the engine will die.


On my EMS interface it reads around 11.6v and with the headlights on it drops to about 11.4v at idle. This is with the car running.

I haven't run the car with the battery disconnected (just the alternator keeping the motor running) as I believe this could damage or cause surges in the electrical supply.

The battery light on the instrument cluster is working (b13/n14) so I'm assuming the connections there are okay.

Where are the fuses I should check? in particular the alternator fuse? I believe there is a 75A one somewhere on the car?

ps: thanks for the reply so far. I'm a little stumped here.

There should be a 7.5amp engine control fuse that goes to the alty, but honestly my rule of thumb is to just go in the fuse box and test/replace all the fuses. They're cheap enough and it takes the guess work out of locating fuses. Also while you're in there, there's a white/red 8gauge wire that plugs into a port on the left side. Thats your alternator feed. Make sure it's in there.

This really sounds like a fuse issue though, so I'd recommend just checking them all. Unless you've recently messed around with the instrument cluster.

Cool I'll check it out today after work. Hopefully its as simple as a fuse.

Just to verify, that small wire with the tiny phillips screw on the alternator is the earth correct? I plan on doing a grouding kit with 4 gauge wire on the motor as well, since I currently don't have any seperate earths on the block or head/manifold.

Yes it is an earth

Are you charging the battery fully? A full battery should be able to run the car for quite a while even without any charging from the alternator. I drove ~50 miles with headlights on, stereo running, fans blowing, etc once with the alternator control connections off (ooops!).

If your batter is dying in a matter of a few minutes, I suspect you have either a bad battery (and even a new batter can fail, if it gets heavily discharged), or you have something that's drawing a *lot* more power than it should be.

Had a look tonight and found the problem. Of the two thick white wires that connect with those two plugs to the positive pole of the battery, one broke off right behind the lug.

So basically yes, the alternator was getting excited (sounds strange), and hence the battery light in the dash was working. The thick red wire from the alternator is the one that connects via one of these white wires with the plug to the positive pole of the battery. It was broken off, hence the power was not being sent to the battery to charge. I didn't spot this initially because I had the wiring kinda hidden for neatness sake.

Battery voltage with the car on is now around 13.3-13.5. With the headlights and fogs etc on it drops to 12.9. I'm wondering if it's a touch low?

Thanks for all the input guys. Appreciate it.

Wow, I wonder how that could have happened. I am in a similar boat myself. I just changed my alternator and the battery light comes on at idle. I am confused as to what to do.