Idiot light on

My battery light came on while running around today. What does it mean and what do I check first?

Basically the light means your alternator is not charging. You need to find out why.

First you might try revving the engine to see if it goes out. If it does, checkthe serpentine belt for slippage. Then, check connections to the alternator and battery. Look for dislodged connectors, frayed or broken wires in the harness, etc. Wiggle things. Then, if you can lay your hands on a voltmeter, you check voltage at the battery to see if it's charging. If it isn't, you can assume you have an alternator problem. If your Jeep has high mileage, as it probably does, it could be worn brushes and dirty slip rings. Take something like a hockey stick or a broom handle, and (being careful not to get your body parts or the stick entangled with moving parts) tap the alternator while it's running. If the light goes out, it's diagnostic for bad brushes. If it doesn't, then it could be that or worse. Either way, you will need at least some maintenance if not replacement of the alternator.

look at the back of the altenator for the wire that is held on with a nut should be a red wire. with the volt meter set on 12 volts dc and above ground the black wire to the negetive battery lug. Touch the red lead to the red wire nut on the altenator while the truck is running and read the meter if it is not at least 13 volts the altenator is bad and should be changed. Be careful tho their are moving parts and hot parts.

I checked the output on the altenator , 12.66volts on start up , 15.2 volts after running awhile. Battery won`t hold a charge over night either.

Then your battery is shot. This can be checked using a hydrometer. Pop the top of the battery and stick the hose end in a cell draw the liquid till it reachs a certain line then read how many little balls float or it may have a tube like device either way it will float and then compare that to the manufactors specs in a fsm or a repair book.

Sounds like a bad battery to me.

If you can get it running, most auto parts stores can test the battery and alternator for you, and tell you which is the culprit.

If it stays running once you jump it, and doesn't try to cut out, but you cant start it again the next day, thats classic of a bad battery. I've even seen them not hold a charge period (meaning that it needed a jump every time you would want to go anywhere...even if the engine was only off for 10 seconds).

Just replace the battery, screw testing the acid.....

Get a sealed AC Delco. Like 70 bucks....

Or an Optima red top!