Leisure Battery practically dead, but why?

[Davidh]

So went out to the van today after a week of not driving it to find the leisure battery was practically dead. (120 agm) Sitting at 11.5v. Managed to get it onto the battery charger and is now charging. My question is what could have possibly drained it, and have I done any lasting damage to it? All I currently have is led lights and some USB and 240v sockets which had no loads on them. Only thing I can think of is the inverter was accidently left on but would this be enough to drain it with no loads connected?
Also my bmv 712 monitor was saying it was at 76 percent! Have I set it up wrong? Thinking on set up I should have put 60ah battery instead of 120ah as from what i understand you only really have 50percent useable space from an agm battery. If anyone could shed any light on this it would be appreciated

 

[Loz]

No damage if you got to it before it dropped below 10.6v for any time
Yes, the inverter could have easily have drained it before switching itself off.
Put a multimeter in series between the battery cable and battery post set up to measure current and measure the draw and see what it is.

 

[Davidh]

No damage if you got to it before it dropped below 10.6v for any time
Yes, the inverter could have easily have drained it before switching itself off.
Put a multimeter in series between the battery cable and battery post set up to measure current and measure the draw and see what it is.

Thanks for the quick reply, glad I got to it then before it then before I had done any damage to it. Will be making sure to keep the inverter off unless its getting used in future. I'll try and get the multimeter set up to see what the reading is. Would you suggest changing my bmv712 to tell it I only have a 60ah battery so this way I will get a more accurate percentage reading?

 

[Loz]

Or an intelligent battery monitor that disconnects the load at a certain protection level?
Better to spend the money on a single solar panel and mppt controller and not have to worry about it going flat?

 

[Davidh]

Or an intelligent battery monitor that disconnects the load at a certain protection level?
Better to spend the money on a single solar panel and mppt controller and not have to worry about it going flat?

I have a victron bp65 but I have mine set up where the inverter runs off a distribution post under the drivers seat which bypasses the bp65. The bp65 only isolates everything coming off the fuse box such as lights, USBs etc. Will need to look at changing this set up. Either that or I could just pull the fuze to the post. I have the ctek 250se with the thought of going solar in the future, just hadn't quite got round to it yet as I thought I would be able to last a decent amount of time off grid as I don't have any big power draws yet. Too many other things I wanted to buy first. Its just a constant game of what to spend money on the van next and the priorities always seem to change