I have learned over the years that a battery in a Jaguar can act strangely. I have seen my engine crank over 'strong' only not to start because of a weak battery.

A few years back when I knew my battery was not the best (just got the car) I was driving and the alternator gauge went all the way to the left and a few minutes later the car stopped. I replaced the battery and the alternator started charging again.

Today the alternator gauge went most of the way to the left but this time I made it home. The battery would not start the car.

My question is can I tell if it is the battery or alternator without putting in another battery? One last piece of information. On my way home the alternator kicked back in for a few seconds.

Thanks for your help.

Jomo

 

A fully charged battery will read 12.75 volts

A 12.0 volt battery is only 50 % charged

with the engine running the large post on the alternator should read at least 13.5 volts , this large post is on the top side when mounted



The voltage gauge on the instrument panel is very accurate but can be off because of loose connections in the main battery cables

The voltage " sag " during starter engagement can not get below 11.4 volts to properly run the ECU , it will still spin the starter just fine