Slik

Started my Jeep to put in the garage before a storm and it made a noise like the battery was very weak. Pulled it in and checked the terminals and fluids since I had the hood up. Tried to start it up to see if it sounded weak again and the whole thing was dead. No lights, door locks, nothing. Checked the voltage at the battery and it read around 3 volts.
I removed the battery and checked it for curiosity and it read 12v. I hooked up the charger and tested the connections again.
As soon as the terminals are touched to the clamps, the voltage drops under 5v. This is with the charger still connected.
i didn’t know where to start so I pull d each fuse from the box by the battery to see if any of them had any effect. It didn’t.
Can someone give me some help?

Thanks

Ghost JK

Sounds like the battery is just done. Time for a new one.

rob_engineer

Yes. Sounds like a bad battery. Reads a 12v float charge, but has no capacity to provide amperage. Our jeep batteries can die sudden deaths. This is well documented on this forum. I too was a victim.

Slik

Thanks. I charged the battery and connected it back to the Jeep. I cranked it with the charger on boost and monitored the voltage. In less than a minute, the voltage dropped to 9. I’m guessing I have an alternator problem.
Does that like a correct assumption?

Jay2013jk

Based on your diagnostic post, when the vehicle is running and the voltage is less than the battery voltage fully charged... Yes.. your assumption would be correct.

rob_engineer

You have not said what the voltage is while your Jeep is running, only when cranking. If your Jeep is actually running you should see around 14 volts. I'm still not convinced you don't have a battery problem. That is much more likely than an alternator for your age of Jeep.

Slik

The voltages are with the engine running.

TheDirtman

Check your fuses, grounds, and the wires coming off the alternator.

rob_engineer

Ok. Then does sound like a bad alternator. Though when you go to the store to buy one, have them check the health of your battery. They will do that for free. That way when you put the new alternator in, you know you're starting with a good battery. I'm surprised at how quickly your voltage dropped, which has me questioning the health of your battery.

Slik

I don’t doubt the battery has been compromised. I believe that if the alternator is the problem, that is what killed it. It made a short trip the day before and possibly did that with just the battery for power.

What is the best way to confirm the condition of the alternator?