This has been going on for a couple of years, my battery loses it's charge over a couple of days, battery has been changed and drop tested, so it's not the battery, when you connect  the battery there's quite a big flash, I put an ammeter in between the negative terminal and earth, with everything switched off it's showing an 8 watt drain, (which sounds like  a light being left on ) I have checked everything (boot light , glovebox light etc) can't find anything that's taking current. I have a solar charger on the dash which helps to keep the charge up, I keep  a spare fully charged battery in the garage and occasionally have to use it, the alternator is charging at 14.5 volts, I've run out of ideas now, I no longer know an Auto Electrician in Wirral, all the good ones I know have retired, does anybody have any ideas???

Sorry no idea but my pure guess is that the battery was starting at 6 year old to be getting towards needing replaces and now at 8 years it will do as it will let you down when the cold weather comes in. 

 

An adult that knows electricery will be along. To me it is all magic. 

I forgot to say the current drain was 800 m/a not 8 watts, which is nearly an amp, the battery is only 2 years old and passes all tests

36 minutes ago, Locomotive said:

when you connect  the battery there's quite a big flash

That could be the cause of your drain.

The big flash is completely normal and due to all the capacitors in the various control modules charging at once, frightening to see but completely normal.

 

It soons drops down to 800ma which is once again completely normal, if the doors are not opened, ignition not switched on etc then gradually all the systems will shut down, you might have 150ma after 30 minutes and more likely 30ma after an hour or whatever, the timings and currents vary on different platforms and according to what control modules are fitted.

 

You will not however be able to see or measure these current draws unless you have fooled the vehicle that the doors and bonnet are closed, if either are open the canbus network will remain active with several modules switched on ready for action which is likely the 800ma that you are recording.

 

Does your vehicle have a towbar with a universal relay for the 7 pin socket?

Edited 26 October, 20223 yr by J.R.

Start by pulling fuses and check whether the 800mA are reduced. Then go to relays.