You've probably sorted it by now, but I had similar problem. My car would draw 250mA when off and locked...I only noticed as I couldn't use it for a few days as I had sent the abs pump off to be fixed. Car only just started, so I looked into it, for me it was the bluetooth/voice control unit circuit board...wasn't shutting off properly for some reason.
Couldn't find a new/used unit for a good price so found the permanent 12v to the board, snipped it and connected to 12v ignition, so only comes on when driving...
P.s. the alarm battery backup is inside the alarm itself...