I have a problem with the battery draining completely down every few weeks. I have tried to do a thread search but could not readily find a thread that fits 50s F100s. If there is then let me know or any ideas?

It is a fairly new good quality ORielly battery. The truck runs and starts fine. Then out of the blue it will not start (even the same day or trip) and the battery drains. I check with volt multimeter and it is down all the way. A full charge from the handheld charger/jumpstarter brings it back, but I never know when it will go down again. Most all of truck is old, stock, except for 12 volt upgrade.

I am far from proficient as a mechanic, especially with electricals but I have checked what I can and have found no drains. Ever use a battery float charger or some type of battery saver on your 12 v truck that I could use until I better determine what might be the cause? Any idea on what could be the cause? It is frustrating and my wife is getting gun shy about going out in the truck.

 

You'd have to have a big parasitic drain for it to go dead in the time frame of one trip, or even one day. I doubt that's your problem. I've had a few batteries fail in my life, and most had symptoms like yours. They work fine after a jump, test fine when charged, then fail randomly. Charge or jump them, and the cycle repeats. I've had both old and new batteries do this.

 

Are you using a generator or an alternator for the 12v conversion? My first suspicion would be the battery too, especially since it is still fairly cold out. A weak or old battery will die when it's cold.

 

If there is a large drain as suspected a float charger will choke. Better to disconnect the battery and keep it charged that way until it's remedied. Auto start batteries do not take a total drain even once, very well.

How are you testing for drain? With your amp meter in series with a disconnected battery cable and post there should be very little current flow, less than half an amp.

 

Check your connections first. Then run down the source of the drain: ignition switch, generator/alternator not charging, bad battery. Personally, I doubt the battery is bad and expect the charging system. While you figure it out, get a portable booster unit and carry it in the truck. This will allow you to jump start on your own.

Use the auto parts guys to check the generator/alternator function. They can also verify on battery function.

 

I would suggest you go to your fuse panel and start pulling one fuse at a time and place the probes of a digital VOM set at the 10 Amp setting on the fuse contacts to isolate the circuit that is causing the possible drain on the battery . Also test the voltage across the battery terminals while the engine is running to see if the alternator is putting out enough voltage to properly charge the battery .

 

If you have a multimeter, an easy first check is to see where the battery charge is when it is not running. The battery should be around 12.5 volts. When running with a good charging system, it should be between 13.4 and 15.3 volts generally. Sometimes, you have to have the engine running above idle before the charging system kicks in.

 

And along with everything that's been said, where is your voltage regulator? Do you have a generator or alternator? As said, maybe the battery isn't always being charged while it's running.

 

A faulty voltage regulator was draining my battery on my 46 Ford car.

 

Something is pulling current from the battery when the engine is not running. One of the quickest/easiest tricks I use is to loosen the battery terminal (+ or -) and see if it sparks when the terminal connection pulls away from the post. When there is something drawing current in the system there will always be a spark when you disconnect the battery terminal and touch it back again. Use oldmerc's technique if you find that there is a draw in the system.

I once had a Cadillac Eldorado that had a battery that would drain down...the battery was good but it kept draining down. I pulled every fuse until I found the circuit that was active...it was the light in the glovebox! Were it not for a good troubleshooting procedure I would have NEVER found that problem.

 

And, don't overlook a sticking or corroded brake switch.

 

Thanks for all the posts. I am going to make a list of possibilities and options and try to work thru them. Wished I was better at electrical.

I have an alternator with the 12 v conversion. The truck is old stock and no dome, glove, or other interior light other than instruments.

My multimeter shows about 12.5 v (engine off and no switches on) after about a 5 hr charge yesterday. After a 15 or 20 minute drive thru town a little while ago the multimeter showed about 11.5 v. I wonder if what seems a quick dieoff is really the overall charge finally getting too low or something else.

I'm not sure how to check the key ignition switch, but it is a little wobbly with the key in - but from the posts it seems it could be most everything. Doesn't seem it will be a quick fix unless luck gives a solution at the first.

Keep the possibilities and what to do coming. Will keep the portable battery charger/jumpstarter in the truck. I'm not going to stop driving it since several grandkids are coming into town next week unless it gets dangerous or quits running.

Keep the idea list coming - something will hit.

 

If you had 12v and you drove a while then had less, I'd go for alternator not charging first. Just my 2 cents....worth about .5v

 

If the alternator was not charging, would the engine die while running? It seems to run fine once started and idling well.

 

As someone already mentioned in a previous post, you should check the battery voltage while the truck is running. You should be able to see it charging and discharging as the regulator regulates it.