After a few years away from BMW, I have recently purchased an E61 525d Auto 2009. Car is great. Some good history from the most recent owner (missing some before that).

One thing I noticed the other morning when I had the door and boot open to load in some stuff, go to start the car and a warning came up with "Increased Battery Discharge". I probably had the doors open for about 20 mins or so, and I guess the interior lights were on, but that was all.

Should I be expecting this message just for having the doors open for a while?

I then did a short run, and when I came to start the car, it came on again. As I got home, I had to wait for a bin lorry, and I sat there with the radio on, without the engine running, probably for only a minute or two, and then a warning came up saying "Battery charge extremely low".

Again, is this normal? 

I have read that a short on an aftermarket tow bar is a common issue, anything else I should be looking for?

Thanks in advance

Morning Steve Welcome to the Forum

Most modern cars are extremely power hungry without the engine running so will kill a battery in no time. First thought is how old is the battery? There is a date on it, if it is the original which is quite possible then it may be dying and need replacing 

Dave