I got my '89 XJS today (love it!), and I think I may need a new battery. Either it just needs to be fully charged due to the fact that the car hasn't been sitting in a garage unused for the last 2 years, or I need an alternator (hope not), or I need a new battery. Is there a particular type of battery I need to get, or is there something that's readily available at, say, Sears (where I get an employee discount).

 

There is only about three manufactures of batteries, just the sticker name is changed. Any good 12 volt battery that is maintenance free will work. But before you do that buy a charger for 40 bucks and charge it. Just make sure that you follow the directions on how to disconnect the battery, how to connect the charger, and how to reconnect the battery, as it is of vital importance that you disconnect the right cable first. Find out if your car is negative or positive ground and then follow the instructions for disconnecting the battery according to which it is negative or postive ground. Use a trickle charger and charge it slowly rather than a quick charge. DO NOT SMOKE NEAR THE BATTERY AS IT MAY EXPLODE, DO NOT USE TOOLS THAT CAUSE SPARK EITHER. DO NOT DROP TOOLS ON THE BATTERY POSTS.
My battery froze this winter and I took it out of my car and brought it into the house and charged it slowly and put it back in the car. And it runs great.

 

Not so fast. Unlike most vehicles, the battery is in the enclosed trunk and requires venting if you don't want to corrode the trunk and have hydrogen bulid up.

You might want to look at Kirby Palm's "Book"...

 

Thanks for the advice on the charger, jetlag700. Haven't had any problems with the battery since I charged it back up to full strength.

Now I just need to get a wheel balanced and a coolant leak fixed, and I'll be rolling.

 

I got my battery from Walmart. Works great. Better price than Autozone.

 

You're welcome ~!
Make sure that you're coolant hoses are not cracked or show signs of bulging, you might overheat your car if they burst, and you DO NOT want to OVERHEAT a V12-EVEN A LITTLE BIT~!~!~! And when you run your car hard and fast and for a long run do not just park it and shut if off especially in a hot summer day, as the heat gets trapped underneath the hood. I crack the hood and let the heat escape as I drive for the last 5-10 kilometers at LOW SPEEDS in town, then when I park I open the hood and let the car idle for a few minutes before I shut of down altogether. NEVER crack the hood if you plan to drive faster than 30 miles an hour as a serious draft of wind might catch the hood at high speeds and tear the hood right off the car~!~! NOT a nice thing to think about eh?
Now some guys might tell you that I am telling you bunk, but it works for me and my car.
I just bought an engine breather filter, spark plug wires and a coolant temp sensor and I am installing them myself tomorrow. Next payday I am buying the distributor and spark plugs. You should change your fuel filter and air filter right away. And if you notice black droplets of water coming out of the tailpipe then it is time to change your mufflers. After I took mine off the tailpipe droplets turned to plain water with no black. I am running no mufflers right now, but that will be remedied shortly. It might not hurt to run a good fuel injector cleaner in your fuel.
And NEVER let anyone talk you into putting gupe or junk into your radiator. The only thing that you should put into your radiator is coolant dye if you suspect that you have a coolant leak, if you shine a LED light on it it will floresce to show you the leak. And DONT let anyone talk you into "flushing" your radiator, it your radiator is not working right then it is time for a new one, a flush might just push junk around and plug your radiator causing your engine to overheat, it there is junk in there it is better left alone until you can replace your radiator.
Never run your Jag if your temperature gauge reads even a hair above N or normal, park the car, let it run and use a hose to shower the radiator, but not the engine itself. That was the advice I got from guys who rebuild V12's and who know alot more than I do about these engines.
Things down the road to change might be the ignition amplifier and you might want to upgrade your ECU, electronic control unit. Adding a cold air intake always helps as does finding some way to modify your car's hood or side scoops to allow the engine bay heat to escape. these are custom things i plan to do this summer. Last but not least grab yourself a good Haynes XJS manual, they only go up to 1985 but they will work for most things. Good luck and let me know how things are going. Donna