Possible Battery Question F150

1987 Ford f150, 302, v8, 5.0, automatic, 120k miles

I’ve been on a year long mission to figure out why my truck stalls while driving, and have researched extensively. One aspect I can’t find much information about is the battery. The truck uses a size 65 battery, but it had a size 24 (still 12 volts) when I bought it, so that’s the replacement battery I purchased, not knowing at the time that it was incorrect. I replaced the alternator a year and a half ago. When it stalled the most recent time, the power windows, radio, and under-the-hood light still worked. However, the good Samaritan that helped me get it off the road listened to it crank and it was a very very slow growl, sounding like a dead battery. He mentioned that it sounds to him like the battery died when I was driving. I put a multimeter on it and the battery was at 11.85 volts (not the first time it read less than 12v after a stall). The truck sat for 2+ hours and I went back to start it, fired right up as if nothing was wrong. I didn’t check the battery then, as I didn’t think of it. I had it hauled to the mechanic and they’re still working on it. In the meantime, I was wanting to learn about the battery, battery related failures, batteries as a cause of stalling, etc. Can anyone share some information about that? I’ve found a little online, but not quite what I was looking for.

Thank you

This is all I have . You should have the proper battery in a vehicle and some last longer than others . Also your vehicle is at the shop so when they have it fixed ask them questions because the answers will pertain to your vehicle problems.

A battery is simply an energy store. It is there to start the vehicle and act as an energy reservoir, if more energy is needed for a very short time, than the alternator can supply. The battery is as large as it it is ONLY because the starter needs a LOT of current to turn. Once it starts the car, the alternator takes over and supplies the current needed to run everything AND to charge the battery.

If the truck stalls from lack of electrical power, the alternator is not working (or not connected). If the battery reads less than about 12.0 volts stalled by the side of the road, the alternator is NOT charging the battery.

If the truck stalled because of the battery, it should read about 9-10 volts. The truck won’t fire the fuel injectors nor the ignition if the voltage drops below about 9 volts at ANY time. A weak or dead alternator and a drained battery is the only time I can connect stalling with the battery.

The way I see it, you have 3 problems - the stalling, a flaky charging system, and a flaky starting system. The second 2 are likely wiring and ground related.

You posted about this before… I assume your mechanic didn’t fix the problem? The best advice in that string of answers was to check and clean ALL the cables and connections to the battery and alternator. I’ll also add - clean all your ground connections and check your ground strap to the engine block.


The issue came back after the mechanic looked at it last time. I’ve been researching the battery and alternator issues (something I didn’t assume was wrong before). If the alternator is bad and it is causing the stalling, will it still provide enough juice to have the lights work? It’s so irritating to not be able to find the solution and instead just find more “potentials” for the source of the problem

The group 24 is only slightly smaller than the group 65. 800 cca to 850 in an Interstate Megatron. If that was an issue it would only be with starting at the very coldest of temps. I am not saying you can’t have a bad battery, just that it doesn’t have anything to do with size. What brand battery did you buy?

I would suspect the cables and connections first. This truck is 32 years old. Plenty of time for corrosion to set in in any climate. Even a heavily corroded fram ecan make a difference in the ground side. Bend your cables with your hands, do you feel wires breaking inside? If you do, and you cut them open, the copper wires will be green.

Get the alternator checked for output and have them run the test after the car has run a while with all the loads you can turn on, and last have the starter checked hot for current draw.