'86 Mazda b2000 bad battery?

Hey all, my old Mazda’s battery was dead when I got on it last evening. I jumped it no problem but after a few miles my headlights were very dim. Like dangerously dim. It was a real white knuckle slow drive home. When I turned the car off in my driveway it wouldn’t start back up again. Is this just a bad battery or is my alternator gone too?

Yes, both probably need replacing. A failed alternator may kill your battery,. Attempting to charge a failed battery can kill an alternator. How old is the battery? Is the alternator the original 1986 alternator? On a vehicle this old, could be corroded battery cables. You should have had the alternator light show on your dash.
Do you plan to do the work yourself?


Yes I plan to do it myself. If memory serves me that alternator is only a few years old. It is no longer my daily driver so goes periods without being driven.

You may have fried the alternator when the engine started and the jumper was removed.

Alternators are not battery chargers, and asking one to recharge a dead battery can destroy a new alternator.

This is the warning that’s included with every alternator I install.


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Suggest you get a battery tender if this vehicle is not routinely driven.


I suggest you invest $20 in a basic DVM and measure what’s going on.
Lots of sources in the internet to learn what to do with it.

Before the first start of the day the battery should measure about 12.6 volts. Then immediately after starting the engine, 13.5 - 15.5 volts. What are you getting?

Now I know.

Right now I’m likely getting nothing at all. Going to borrow a charger from someone and grab my multimeter from work Monday. We shall see.