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?

voltage regulator or a new alternator. Alot of alternators dont even kick in until you're around 1100rpm

Alternator

well. the thing about my alternator is its brand new and was tested about one month ago. the conclusion was the battery would not hold a charge. the alternator was running perfectly. under load, the old battery died. now... i have the new battery and its acting like it wants to go.

make sure your cables are in good shape.

Determine if your alternator has an internal voltage regulator, such as the early XJ's did, or uses the PCM to control the alternator. Late model XJ's (year???) use the PCM. Your symptoms indicate regulator. If the your regulator is internal to the PCM, a new alternator won't help.

The 2001 Cherokee has an external voltage regulator (internal to the ECM) controlled by the ECM.
These are similar conditions that I had on my '98 when one of the diodes went bad...
Tested the alternator with my Smart battery charger and then had it verified at the local Goodyear dealer with a SnapOn system tester...
Replaced the alternator with a '98 Grand Cherokee 136A alternator and the system voltage under full load never drops below 13.6VDC...
The installation of a 136A alternator over the stock alternator does require the upgrade of the charging lead going from the alternator to the PCM.

Tighten your fan belt first.