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81 Toy Pickup is using up batteries faster than gas!

My alternator is fine. My truck runs, then slowly dies, if the lights are on they fade, and ultimately it dies, not good when you’re driving down 91 in the dark. I can jump it to get me to the parts store where I exchange the brand new battery on warranty. The battery is dead. Again, and I cant strees enough, the alternator is fine. I replaced the voltage regulator, I have not checked the fuses. My positive terminal needs replacing, but it is different than what the parts guy brings me. Has any one had this problem, or who is savvy enough to answer it straight out on theory alone?

A mechanic is savvy enough to fix it without excessive theory. Save the theoretical considerations for something more challenging—like better fuel economy.

Is the red alternator warning lamp on the dash working? If not, the alternator will not charge.

With the key in the RUN position and if the alternator lamp is working the pulley on the alternator should be magnetized. Touch the pulley with the tip of a screwdriver to verify this. (key on, engine not running of course)

If the dashboard lamp is working and the pulley is magnetized then you should consider the possibility of a blown fusible link between the alternator and battery.

That’s a few quick backyard checks that may help but you did not state if you have a VOM or not.

All the parts people do is hook-up a device to the battery if it says “bad” they replace it,we need to know why the battery is bad. I like the conductance test or the load test. Don’t trust the parts store to provide the info. to solve this.

The good ones can/will also do a charging system check.

Your alternator is NOT fine. Or, you have other bad issues with the charging system. The battery is used to start the truck, then the alternator produces juice to recharge the battery and power the trucks electricals. If the battery dies while the truck is running, and the truck dies with it, there is no amperage coming from the alternator. Your killing these batteries by running them completely dead.

BTW, how did you determine the alternator is fine? Did you have a charging test done? A bench test?

I had a '90 Toyota truck that had an alternator that was turning on and off. Turns out the brushes were worn out, and would sometimes loose contact with the stator inside the alternator. It bench tested fine twice. But, would crap out once the engine was warmed up. Replacing it fixed the problem. I guess 275,000 miles was just too much for it.

I will check those! Thank you.

Are you getting 13.5 to 14.5 volts DC across the battery terminals when the engine is running? When you get that voltage consistently, you know the charging circuit is okey. If not either the alternator is not producing or the wiring from the alternator to the positive battery terminal has high resistance.

Hope that helps.