A little more than 2hrs ago I put my fully charged (12.7V) AGM battery back into my car. I haven't started it or done anything that would draw any power other than opening the boot to get a reading from the battery and to my puzzlement has dropped to 11.90
probably a stupid question but is this just the case of **** battery or is there something else possibly happening because that seems excessive for that time frame

 

You need to test the battery first. A Medtronics or similar, not the old carbon pile type.

https://www.jbtools.com/midtronics-m...4aAicKEALw_wcB

If the battery tests OK do a draw test on the car.

https://www.wikihow.com/Find-a-Parasitic-Battery-Drain

Could be a bad cell in the battery. Could be the car isn’t going to sleep fully when you lock up. The Body Control Modules can wig out. There could be water leaks from the sunroof and cowl that corrode a module. Check under the carpets and in the trunk. Make sure you are charging the AGM battery with a charger that has an AGM setting. Could be the car charging system is not set for AGM.

 

Almost guaranteed to be a current drain in the car. See if you can find it using Robtrt8's excellent link.

You do understand that by opening the trunk you have woken up the car?
I usually wait 45 minutes for the car to go to sleep and then look for current drains. If you leave the trunk open it will cut off the power after 30 minutes or so but any little disturbance from you hooking or unhooking things will start this all over again and you will need to wait an additional 30 minutes.

The only way I find these is using a clamp on DC ammeter that can read as low as 1 ma. Most car manufacturers will give a maximum current draw while asleep of around 30-50 ma.. You need to a meter that can measure in that range.

Can you report back with how much current your car is consuming?
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