Electrical gremlin...help?

Ok all you Ranger guru's out there.....I got one for ya. I have a 95, 2wd, 2.3 5 speed ex cab short bed. About a week ago, battery started to lose power (Slower cranking over the course of a week) and finally went dead while I was at work. I got it started, drove it around for over an hour, and the volt gauge read normal. Went to fire it up, dead. Got it running again, and parked it, chalking it up to a bad starter based on the volt gauge reading ok. Pulled the battery, threw it on the charger, and left it for a day. Once it was charged, I put it back in the truck, and for grins and giggles, fired it up. Started and ran like a dream. Threw a multi-meter on it, and battery is reading 12 volts, it drops to 11-ish when it starts, but once running, the meter reads almost 15 volts. However, I am noticing it starting to run out of juice again when I start it. I think the battery is gonna die again. I am very confused. Anyone have any idea on what my electrical gremlin is?

I'm not a guru. The 15V reading indicates the alternator is working. It sounds like the battery is old and not able to hold a charge.

Richard

Sounds weird to me. 15V sounds high if that is really what is there when the car is running. If alternator is putting that out I would wonder if the regulator is failed.

It almost sounds like an overcharge situation but one part doesn't make sense. Too much charge current (caused by too high voltage applied when charging) will damage it.

If the battery gets overcharged, what you experience isn't so much a discharged battery right off. It will be changed but capacity is lost. You will lose cranking amps however till the point where the voltage will just drop.

BUT taking it out putting it on a regular charger doesn't off hand make sense. That is more consistent with a battery with low charge when alternator is not charging.

So I am going to take a wild guess. Maybe your battery terminals are not making good contact/corroded? That when you start the car the current comes from the battery, but your alternator connection at the battery is open. The 15V might make sense from the alternator if alternator wasn't connected to the battery so no load.

Taking battery out and putting back in should have resolved the corrosion issue at least temporarily unless there is a problem where the clamp on the battery terminal is tightened all the way and just isn't holding tight.

Where did you measure the 15V? At the battery itself or someplace else?

When I have had bad battery connections I been able sometimes to measure voltage at the center of the battery terminals themselves yet see a slightly different voltage at the cable clamps on the terminals.

In the explorer I don't know know if the voltage in the dash provides real readings or fakes a few states (like the oil pressure guage). What matters to me is the voltage on the battery terminals using an actual voltmeter. Usually I expect 14V when car is running or a little more but 15 is clearly too much in my opinion and sounds more like an alternator not connected to the battery.

15V is high and indicates one of two things.

1) The regulator has failed and it is juicing the battery and killing it

or

2) The battery is shot and the alternator is trying to compensate and get it charged.

Either way you need a battery, so start there, but be prepared to replace the alternator immediately if the charging voltage doesn't come down between 13 to 14 volts with a new battery.


Also, the alternator is NOT A BATTERY CHARGER!!! I have seen vehicles (including Rangers) burst into flames because people thought that driving with a dead battery to charge it up was a good idea.