I have a 2000 XJ 4.0 with 150k miles. The electrical accessories I have include upgraded H4 headlights with harness, (2) 130 watt KC lights wired in with high beams, stock fog lights, and heated seats.

My current battery is an Autozone Duralast Gold with 800 CCA, it is about 1 year old. This replaced my Optima yellow top after it failed.

I have recently added Jeepers and Creepers battery cables, 5-90's alternator cable with 200A ANL fuse, and a 150 amp alternator. The alt is a stock sized case rebuilt to handle 150A.

Ever since this winter hit, my Jeep turns over slow. I thought it might be the starter, but the Jeep only cranks slow on a cold start. If I drive somewhere, then park it for an hour or two and come back it will crank right up. If I'm driving and turn my high beams on (with the KCs) everything is fine. If I turn the high beams (and KCs) on while sitting idle at a stop sign, the lights will dim and the volt gauge will drop to 12 volts. Turn the high beams off and everything goes back to normal at idle. If my electric fan comes on with just the head lights on, the battery gauge will dip to 12 volts again.

I never noticed this with my Optima battery and stock battery cables. Is this an electrical system problem or just a crappy battery? I tested the battery with a load tester and it tested OK, but that was also after driving it for a bit. Battery terminals have been replaced with brass terminals.

I'm stumped. Any help is greatly appreciated.

 

If you have problems while running I would suspect something in the charging system and not the battery. You shouldn't drop that low while running especially with that setup. The slow turnover is obviously related to the battery but it could be it's just not getting a good charge while your running. Maybe someone a little more knowledgeable can offer a more technical answer?

 

You replaced the alternator cable, what about the battery and ground cables? What do the connectors at both ends look like?

 

I also replaced the mains with the Jeepers and Creepers cables (welding cable) and cleaned all the connections and grounds with a wire wheel Dremel. The battery terminals are clean and I have brass connectors. Everything is tight.

The alternator charges fine if I give the engine gas.

If my electric fan turns on at idle with my head lights on, the volt gauge will spike to 12 volts. If I put the Jeep in park and rev it up to 1000 RPM everything goes back to normal. I don't have any problems with all my lights on while cruising. It only happens when I am idling.

 

How old is your belt, and is it properly tightened?

 

The belt is 4 or 5 months old and is pretty dang tight. That is actually the first thing I suspected since my buddy had a problem with the belt being loose on his XJ and slipping when the A/C compressor engaged.

One thing that strikes me is how this problem definitely worsened when I went from my Autozone rebuilt Alt to the new 150A alt. The 150A alt was swapped in 3 days ago, and the problem has gotten much worse immediately after the swap. I'm thinking my "high amp" alternator is only producing power at higher RPM, and my Duralast junk was only mediocre to begin with. I never had these sort of issues with the stock factory alternator (before the bearing started making noise) and the stock crappy battery cables.

 

I would check the voltage with a multimeter while its idling. Most alternators will put out 14- 14.5 volts. Check the voltage right on the battery terminals.

 

I'll have to borrow a multimeter. According to the dash gauge it puts out 14v at idle. The voltage only drops to 12v when I apply a significant load at idle such as KC lights or my electric fan kicking on.

 

I would start by rechecking all cables, grounds and connectors with quality of their connectors made.

 

I checked all the connections and everything is clean and tight.

 

Here is a video showing what happens:

 

I'm not impressed with the battery you have. I have one of those "Gold" type, & had it replaced under warranty, after I raised hell with the store. And it's still junk. Duralast name seems to be stretching the truth a bit....

 

I think you found the problem already ^^.
If the voltage rises with RPM, that's the alternator. It does not appear capable of supplying sufficient current for all your accessories at idle speeds and your battery isn't stiff enough to supply it either.

 

"Last in Durability", lol.

 

I did a few tests with my battery load tester this morning. I have noticed within the last month or so that the Jeep will crank very slowly after sitting over night. This is even more apparent with the colder ambient temps. If the Jeep has been running recently (like stopping at a store for a minute) then it will crank right up fairly quickly.

Here is what the battery shows after sitting over night. The Jeep is stone cold and hasn't been run today. It shows about 12.5 volts.




Here is with the load tester clicked "on" to put a load on the battery. The battery is an 800 CCA battery, and is bordering on the weak side. I have done this test after running the Jeep for a bit and it will test a bit higher, but still closer to the weak side.





And here is the voltage reading after completing the load test. It is reading a little bit lower than before the load test.





I'd also like to add that this battery was fully charged by a 2 amp battery charger about 2 days before.