99 xk8 bought in july, 2011. Bosch battery group 49 has been working fine! I don't see any markings on it to determine it's age. I thought I might take it to Pep Boys, for a free test, or is the gauge on the dash reliable enough to go by? The manual says with ignition in position "11" and car not running, pointer needs to be between 9 and 13 volts, between 13 and 17 when engine is running above idle. Would you trust this gauge without further testing?......Mick

 

At Pepboys they will test the battery under load...it is a more reliable indication of the battery health.

 

If you've got a digital voltmeter, a somewhat less accurate measurement can be done at home. (This one is about as accurate as the hydrometer measurements we used to be able to do before sealed batteries.)

Description here ... http://www.scorekeeper.com/jaguar/jaguar02.htm