Voltage drop under load

2001, 4.0, AW4, NP231, 183,XXX miles. The last couple days the temp outside has been well below freezing and it has been slow to start. It normally fires on the first crank and if it sits for 4 hours or more it cranks slower when starting. The battery is 2.5 years old and so are the cables. The connections are all good. Right after I shut it off after driving for 20 minutes, the battery showed 12.65 volts. After sitting for 4.5 hours it showed 12.19. While starting it dropped to 9.11 volts and then jumped right to 14.4 and stayed there while running. Is that voltage drop normal or do I need a new battery?

You measured the voltage while starting? If so, I'd say that's OK. The only one of our XJs that I've ever checked voltage on after sitting a while is our '96 Classic, while diagnosing power window problems, and it was sitting in the low elevens, after not having run a few weeks. It starts right up, and the voltage goes right up to about 13.8-14v, till the battery's happy, then floats. Possibly you could have the battery load tested, as batteries just don't seem to last as long. I've been using Interstates for the last twenty years, and seem to get at least ten years out of a five year guarantee battery.

Given the charge voltage and the at rest voltage, the battery appears to be fine.

The best thing you can do is to replace the stock cable with upgrades. You might be amazed at the difference. I had mine made at my favourite battery shop but 5-90 here makes them as do others. I use military style battery connectors so that the connectors and the battery posts are not buggered up every time the battery is disconnected. Keep the grounding points clean and all should be well.

The ossue with lead based connectors is that they stretch every time they are over tightened and eventually,the ends meet and they no longer properly secure the cable resulting in a poor connection. Another thought would be to go to a no-lead style of cable.