Based off of that comment I would be leaning towards the alternator rather than the battery. I actually just had to replace the alternator in my '99 XJ this weekend. I went to start the XJ Saturday morning (~35 F) and it barely started, it took 3 tries and then I had to throttle it to keep it running for the first minute or so. It had been getting progressively harder to start in the mornings too, and had been turning over slower, and I had been suspecting the Alternator was dying for the last few months. After a few tests with the volt meter, I was 99% sure it was the alternator, so I pulled it and had it tested at the local parts house, and sure enough a bad diode, just as I thought. I put the battery on the charger; luckily itÆs a deep cycle battery so it still seems perfectly happy. I put the new alternator in on Sunday, and the XJ starts and runs like a champ now.

Sean