Looks like the regulator in the alternator is bad and allowing to overcharge... This could cause the battery to overheat and pop... Unless there is a short within the battery, and have the alt overcharge, but its very rare...

Or its bad gauge???

You have a muti-meter to check at battery when idling at normal temp???? Should read around 13.8~14.2 volts..

 

Batteries and alternators have a symbiotic relationship. When one starts to go, the other tends to over compensate. The problem is determining which comes first?

My advice first thing is after running the engine and shutting off, is if the battery shows that 15.8 vdc, is to turn on your head lights for about 30 seconds and turn them back off. This will take the surface charge off the battery and get it down to what the state charge is. Check the batter again for voltage and it should be about 13.1-13.2 volts. I would then check again after about 1 hour sitting and the battery voltage should be about 12.6 volts for a 100% charge to about 12.1 volts for a 25% charge.

Anything over 14.7 volts charging runs the risk of boiling off the battery cells. Either way, I would get your battery out of the vehicle take it down to AutoZone or other like chain parts store and have them load test your battery. If failed, get a fresh one installed and recheck your alternator charging voltage, it should be between 13.8 volts and not to exceed 14.5 volts. If it is still over charging with a fresh new battery or battery that has tested serviceable, I would then look at the alternator replacement.

 

Back in the day a Battery Load tester cost too much for most people to justify owning.

Now you can catch one on sale at Harbor Freight for twenty bucks.

 

Thanks everyone!! So far what I have found out is

1) my Multi meter was bad! I used another one i had and truck off battery is @ 12.5 Volts Good.

I did not check truck running yet to see what alternator is putting out. But the truck gauge is ok one time another its either high or low? My gas gauge is now allover the place also either says i have 3/4 of a tank and i know i'm lucky if i have a 1/4 actually. Then it will go way past empty the next time. Maybe i have a short somewhere.

 

A couple of things to consider:

1). Age and condition of the battery (need replacing?) 4 years on the factory original if you're lucky. Don't get another factory battery.

2). Did you heavily use it right before that happened? For example, several hours of sound system use in accessory position.

The gauge indication you had indicates a high rate of charge, and not necessarily a problem. Keep a reliable multimeter handy if it does it again. Also, if you go to most of the chain auto parts stores, they will load test your battery. Voltage alone does not tell the condition. You can have a battery with dead cells that will measure at 12 volts.

As an aside, some people think a good test of an alternator is to see if the truck keeps running with the battery disconnected. DO NOT DO THIS. An alternator is not a generator, it requires DC battery power to work properly, and actually generates AC power that is converted with a rectifier to DC for the charging system. The reason for this is to get consistent power at all RPMs, from idle to red line.

As far as multiple gauges acting flaky, it could be a ground problem.

 

Just an Up date.. Thanks so far with all the input as well.

I bought a tester from HF and it says all is well the battery and the alternator. I will keep an eye on it and see what happens.

 

Well so far everything seems ok but Sunday i went for a drive and the voltmeter went pegged to 19 volts the whole time. I get home let it run and check with my meter and it says 13.5 volts running?? Not sure whats up.

 

Well, when you check it with the mutimeter and the vehicle gauge was still at 19 volts, my guess would be a faulty vehicle gauge..

The only way to really tell, is to take it to a reputable shop with a portable diagnostic tool plugged in the OBDII port and take it for a drive and see if it can be duplicated...

Good luck