battery experts help please!!!

2001 Cherokee
4.0 L Inline 6
NP241

I'm not sure what's wrong with my battery and was wondering if I could get some helpful input. I have a brand new battery installed. Its maybe two months old. At idle, with nothing running except the jeep, i'm at 13.5 volts. When I turn on my radio,a/c or heat, and especially headlamps, my vots drop to 11 and sometimes 10.5.

Tonight I had the heat blowing, lamps on, and radio on and the volt meter dropped to 9 at idle and my check guages lamp came on. Then it shot back up to 11. I pressed the gas to about 1500 rpms and my dash lights and headlights got brighter. When I let off the gas they got dimmer plus the voltmeter dropped.

Can anyone help me diagnose this problem?

So, when you put a load on a finite source of power (battery) the voltage drops?

I want you to follow this link and consider some of the advice provided: http://www.olypen.com/craigh/charge.htm

This article will explain what your gauge is doing, and what you can do to improve the charging of your battery.

My voltmeter on the dash reads 11vdc and with a Fluke 77 multimeter at the battery reads 14.0vdc. Only use the dash guages as a suggestion. I figure the dash wiring on the 21yo XJ has high resistance due to corrosion. Yours sounds like a problem beyond high resistance.

Put your volt meter (+) lead right on the altenator output lug and measure there. Normal output should be 13.5vdc to 14.5vdc. Then measure the voltage at the battery to determine if there is excessive voltage drop. Check the belt tension, but it would probably be squealing with those numbers. If when measuring at the alt it still reads below 13.5vdc with a load then it sounds like a voltage regulator or tri-diode not working.

thanks for the link. very useful.

Oh yeah, there is a temperature sensor under your battery. The PCM uses the battery temperature to determine how much charge to send to the battery. Maybe it was damaged somehow in the battery RR and is causing the erratic charges.