How does a battery work?

[Esther]

I have a dead battery in my 1986 fj60. I am trying to figure out what is going on. Last Saturday my wife left the lights on and the truck needed a jump. No problem there, she drove it home and parked it. When I went to start it a few hours later, it would not start. I got a jump, then took it up on the highway for 20-25 min to charge the battery. All was fine until we were out a few days later and it died again. Another jump and we are on our way. Now, this morning, another dead battery. The dash volt meter reads zero. After a mid week charge, it was above 12, and around 13 or 14 when the truck was running.
Something is not charging the battery or something is draining the battery while the truck is at rest. My question is what charges the battery while the truck is running? Another question is can the cooling fan on the driver side just in front of the firewall drain a battery? The thing seems to run for a long time after the car is turned off.
Also, does it sound like an ignighter problem to anyone? I always thought that the ignighter either works or does not work. No intermitent stuff like what I have going on.
Looking forward to the replys, and thanks.
John
PS, the battery is 2 years old.

 

[Gabbo]

Mine does that sometimes, but I've found that it's not the battery dying it's the positive battery cable connection getting loose. So I take it off, clean it up, and tighten it back on. I should just get a new one. Try checking that before you drop $ on a new battery.

 

[Wile E Coyote]

What charges the battery while driving is the alternator. The issue seems to be that your problems started after the battery was drained by the lights. Also, the truck will run after a jump start. I'm of the opinion that your battery is dead and will no longer take a charge, assuming your cables and related connections are sound.

 

[Esther]

Yeah, checking the battery is on the to do list today. The cable is tight and clean, but I will double check just to make sure.

 

[Wile E Coyote]

Yeah, checking the battery is on the to do list today. The cable is tight and clean, but I will double check just to make sure.

Don't worry if it's tight or not, as much as if there's a layer of crud under the terminal impeding conduction. Looking at the exterior of the insulation only confirms the exterior of the cable insulation is pretty. Grab the cable where ever you can get to it and feel for hard sections, or really soft sections. Feel for bumpiness under the insulation, or cracks that weren't apparent until you flexed the cable. Copper corrosion tends to appear green, BTW. The lead terminal or post will tend to have fluffy white deposits.

 

[Dynosoar]

Once a battery has been run dead it will never fully recharge again. Unless it is a deep cycle type of battery.

Dynosoar

 

[LoneRanger]

maybe a dumb question, but have you checked the fluid level or tested it? You can buy a cheap, easy to use test kit from autozone which will tell you if your electrolyte is holding a charge.

 

[Esther]

OK, cables are in good shape, no soft spots or cracking. No white dust at terminals. Fluid is good. I am going to take the battery to Napa and have them look at it. I just hope it is not the Alternator.
John

 

[NLXTACY]

Once a battery has been run dead it will never fully recharge again. Unless it is a deep cycle type of battery.

Dynosoar

Exactly right.

In very basic terms, when a STARTING battery is allowed to fully drain the first time, its fully charged capacity drops from 100% to around 90%. The problem is its that first 10% that is crucial to a starting battery. Now if and when that battery gets discharged fully again, it drops now from 90% "fully charged" to about 80%. Anything below 70-80% of its fully charged capacity and its usefulness goes down the toilet. Deep cycle batteries do not have this issue, BUT they are NOT designed for rapid discharges which is what a starting battery goes through.

Get this book and it will tell you way more than you've ever wanted to know about your battery:
Amazon.com: Managing 12 Volts: How to Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems: Harold Barre: Books

 

[Esther]

OK, here is what I did and am planning. I trplaced the battery with a new one and the truck started AOK. Before I turned it over, I noted the volt meter on the dash and it was reading 12, the old battery read 0 this morning. With the new battery the truck started fine. Now, to be safe, I bought a napa alternator new, but did not install it. I plan to drive the truck for a week with the new battery only. If the alternator is not working, I wll know for sure when the truck dies again. At that piont, if it ever comes to that, I will already have the alternator and tools in the truck, so I can change it on the spot.
How does that sound? good plan or not?
john

 

[NLXTACY]

DO NOT trust the volt meter on the dash. Get a hand held volt meter and check what the charging voltage is from the alternator before you do anything else. Test it at idle and test it at ~2500rpm

 

[inkpot]

DO NOT trust the volt meter on the dash. Get a hand held volt meter and check what the charging voltage is from the alternator before you do anything else. Test it at idle and test it at ~2500rpm

Howdy! Sounds like a good plan, having the new alternator for a backup, just in case. Even an inexpensive volt meter will give you readings that are accurate enough for battery testing. Just take the readings right off of the battery posts. It should read a little over 12 volts ( 12.25-12.75)when the engine is not running. If the alternator is working while the engine is running, the battery voltage should read between 13 and 14 volts. Some cars read 14.5+, but that is still OK. John

 

[Esther]

I think all is good. Thanks for all the replies and sharing knowledge.
Here is what I just did. I went to Napa and had them put a meter on the truck. At idel it was 13.8, at 2500rpm with all light, flashers, AC, wipers on, it was at 13.5.
I then drove down the road to Checkers and did the same thing and had the same results.
I am still keeping the new alternator in the box for a while just incase I missed something.
Thanks again for all the tips.
John

 

[NLXTACY]

Awesome!

 

[sl33py]

I think all is good. Thanks for all the replies and sharing knowledge.
Here is what I just did. I went to Napa and had them put a meter on the truck. At idel it was 13.8, at 2500rpm with all light, flashers, AC, wipers on, it was at 13.5.
I then drove down the road to Checkers and did the same thing and had the same results.
I am still keeping the new alternator in the box for a while just incase I missed something.
Thanks again for all the tips.
John

I'd have spare Alt just in case too, but rather than get a napa alt, get a Nippon Denso from the parting out section. That's what i did - half the price and worth more than the napa to me. New ND (reman'd) are 140'ish iirc.

GL!

rob