Auxiliary Battery Charge

Rob22 · October 29, 2023

I am charging my Auxiliary at the moment one lead on the positive post and negative to ground.

My Auxiliary was 5v to begin with so i realise it probably needs replacing but i kept on charging with my Ctec.

I also checked my Main battery only to find that it had gone up to 12.4v (Previously it was at 11.6v ?

Is it possible that the voltage has gone from one battery to another. (2013 F Diesel.

Thanks

Rob

zedebee · October 31, 2023

Can't answer your final question. However I think it is probable that both batteries may need to be replaced. Assuming they are not being drained by something else on your car.

Recently I replaced mine when main battery was at 12.2 and auxillary at 9.6. Both original from 2014 and at 9 years of age I was happy to renew!

Age of your batteries should give you a further indicator.

Big John · October 31, 2023

Hi

Possibly due to your timing.

The main battery takes a while to come back to its steady state voltage when a load is removed from it. If you unlocked the car and then opened the boot, the car will have "woken up" and started powering up various modules. If you then read the main battery voltage the car was probably drawing in excess of 10 Amps so the voltage will have dropped to 11.6v. If you then just left the car with the charger on the secondary battery that battery will have started charging. As time went on the car will have started shutting down the modules as you had not started it, but this can take quite a long time. If you then simply re-checked your main battery voltage without again unlocking the car the modules should all have been asleep, allowing the main battery to recover to 12.4v.

However, 12.4v at rest is pretty low for an AGM battery so you could well be due a replacement for both. My 2013 Sportbrake is now on its second Secondary, and third main battery.

J

Rob22 · October 31, 2023

Thanks John I think that at the end of the day I need to replace the batteries

Been trying to bring them back to life to save the £607 my local Jaguar dealership have quoted me for both to be replaced. Thanks for you advice its always a pleasure John.

Rob.