Mark Doiron

I know it's a small pain in the rear, but if you pull the alternator you can have it tested at many auto parts retailers. AutoZone will test it free at many locations around the U.S. Better to find out now that your alternator is bad than to damage another battery. To be honest, however, with the age of that OEM battery, it's probably the only thing bad. Still ...

Lorrel

If I read this correctly with the vehicle running, the voltage reads 14.2 VDC. That would lead me to believe the alternator is good. Static voltage on the battery when not running is 6 VDC. Bad battery!!!!!.
As RonJenx has stated " The JK won't run on just the alternator. If the PCM detects too low a voltage, or no voltage as when the battery is disconnected, it will shut off the generator field. Your JK starts and runs when the jumper battery is connected, but will shut off as soon as the jumper battery is disconnected, due to the battery being discharged. Take the old battery out, and connect a known good battery, (not one that is still in a jumper vehicle), and read the alternator voltage while the engine is running".
As always RonJenx has very good information and I believe he is correct on his assesments at least 99% if not more.
Go get a new battery.

Mark Doiron

I agree it is likely just the battery because of age. But, and I'm open to being corrected of course, even if the alternator puts out proper voltage it could still overcharge the battery, causing the swelling OP describes. Yes?

Lorrel

Yes that is true, however I believe the charging voltage of the alternator should be between 13.5 to 14.5. With that said I believe a constant 14.5 would seem a bit high. I have checked my battery many times with readings of 13.5 to 13.7 static, and 13.7 to 14.6, depending on conditions. At any rate, a battery with a static reading of 6 VDC is dead. As far as the swelling I agree one cause could be over-charging, but then again if 1 cell or two would be dead, I could believe some other cells that are being charged could swell.
The first step would be to get a new battery, Once installed check the charging voltage and if a constant 14.6 or above have the charging system checked

Mark Doiron

Thanks. And I agree the battery is probably going to fix things.

scooby snacks

My symptoms were going same. Working one minute not working the next. Battery was toast on my 2012. According to the battery guy he said these batteries do not like to be jostled all the time so wheeling kills them. I purchased an Optima Yellow Top using a 20% off coupon at Advanced Auto. No problems since.