kept displaying battery and key batteries are low, need to restart engine, but both batteries checked out fully charged. Do I need to reboot its onboard computer? How to do it? Is it safe to do so? Do I need to get it done with service?

Victor

 

The warning about key batteries will be fixed by (wait for it...) putting new batteries in the keys.

 

No I checked out that battery with my meter and it was fully charged.

 

Is your main battery an AGM type of battery?

 

VictorLam, the watch battery that is in the key will show a high voltage, even near the end of its life. The trick is that when you use the key, the voltage will drop considerably. hence the message about a low battery. Replace the battery in the key and all will be good.

As for the main battery in the car, this is normally a message that comes on when you sit somewhere with the car turned on electrically, but leave the motor off, and then sit there for say 20 minutes or so. As a battery gets older, it develops an internal resistance which is going to result in the output voltage dropping quicker. We are only talking but 0.1 VDC here. This is where getting a load test of the battery will be the true answer to the question of whether you need to replace the battery or not. This puts a big load on the battery momentarily and it measures how far the voltage drops. The general rule that I have found that works with Jaguars is that if the battery drops to loss than 75% capacity, it is time to replace the battery as it will start causing random errors with the car. You wlll be amazed as to how much faster the engine will crank over when you put a new battery into the car.

 

I had the same thing on my 2015 Jag XJL. Kept recharging. but the low battery message on the instrument panel wouldn't go away. The solution is buying a iCarsoft Multi System Car Diagnostic Tool LR V2.0 (specifically made for Jaguar/Land Rover). You can reset the warning with this and also the oil service warning.

 

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