Battery Charging


With our Modern Jaguars requiring a lot of battery power I wanted to share with you some information about charging.

A number of weeks ago the electronic hand brake would not release on my 2004 S type.  Our car batteries need to be fully charged, but carrying out lots of relatively short journey’s with everything running or not using our cars frequently enough saps the power away.

I put my optimiser battery charger on my battery for 24 hours thinking it would charge my battery, it did but not to full capacity, let me explain.

Modern batteries are now quite large; for example, my battery is a 12v, 150amp / hour unit. I have a 6amp hour normal battery charger, this means:

150ah / 6ah  = 25. Which means to fully charge my battery I would need to charge it for 25 Hours. 

Lets assume my optimiser is a 0.1a trickle charger:

150ah / 0.1ah = 1500 (hours), so that would take 62.5 days to fully charge the battery.

So realistically I had only charged my battery for 24hrs x 0.1amp = 2.4amps obviously enough to release the hand brake but not to fully charge the battery. I thought at this point that the battery needed replacing, it was only when I connected my 6a charger for 24hrs that it fully charged the battery, it’s been fine ever since, until next time!

Taking these things into account you would need to know the battery amp size (different amp hour batteries can be fitted) and the amp hours of your charger (Written on the charger and battery), Please note, some large chargers can be as big as 25ah meaning it would take only 6 hours, these however high amp hour chargers can cause the battery to overheat which may shorten the life of the battery.

So make sure you also have a decent charger if you have not got an optimiser permanently plugged in.

~ Dave Knockold ~

© Surrey JEC 2019