Battery’s been randomly dying not sure why.

[Dragonsyph]

My car has went completely dead a few times this year and I got a jump and was fine.  
 

But yesterday I hooked a 3.5 amp charger and left it for well over 15 hours.  When I went to bed it said it was at 50%, when I get up today for work and take it off, it was back down to under 25% according to the charger.  
 

Nothing is on from what I can tell. As most things like lights etc will auto turn off after set tile anyways.  
 

Is one of my battery’s bad?  Or do I have some sort for hidden drain?  
 

Anything I can do to trouble shoot this?

[liteblue]

Similar thing happened to me. It ended up being a bad battery. 3 year old agm that was abused. 

 

You say one of my batteries. Do you have two?

 

If yes try disconnect one of them and using just one to run your vehicle. Then charge your batteries. Check battery voltage the next day. If the open battery looses charge overnight, it's bad. If your car does not start then the battery still hooked up to your car is no good. 

 

Testing for parasitic drain can be tedious. Use camp on main ground. If more than one ground off of the batteries multiply current by number of grounds. Anything higher than 100 miliamp is worth investigating. 

 

 

[Dafaseles]

How long have you had those batteries? Has this been a problem the whole time you've had the car or is it a new problem? When did the problem start? Are you also running an isolator between batteries?