Hopefully i can help..
I take it from your question that your battery continually goes flat - several reasons can cause that and seldom use can be in some cases a contributory factor if the car only goes a few miles and back - However another cause could be the battery itself - depending how old the battery is in the car - it maybe time to re-new it if its not able to hold a charge anymore..something you may want to have checked out aswell as the performance of the alternator to ensure it charging properly when the cars in use..Another cause could be that you have something in the car drawing voltage when the car isnt in use/parasitic battery drain which is usually a component within the car drawing current from the battery whilst the ignitions off or the car is un used - for example routine check would be check all exterior lights "including number plate lights which are always missed out" and interior lamps , glove box "if any"/ boot lights are not still on when the cars not in use or locked or any other items plugged in make sure it disconnected also check on any aftermarket fitted accessories are properly wired in - the next stage ideally would be to do further testing to trace down which circuit is at fault..I do hope this helps..If you need to ask anything else or include anything further then just continue before you rate
just another thing please;I want bay a portable car battery starter,as my car battery is in the boot,could you please tell me how will I connect the starting battery- pack to it?i know that the BMW has a starting point in the engine,but how can I connect them up? I will be very graetfull for your answere.
Yes there should be a jump starting point within the engine bay on the E39 which i asume you have on that year from what i recall there will be like a plastic cap with a + on it pretty much on the inlet manifold once you remove that then you should see - the metal contact to attach the red positive jump start lead too..the other black negative lead can go to a good clean ground metal point on the engine cylinderhead/block..either on the engine itself at the front corner - passenger side small metal bracket there..or one of the 3 visable bolts on the top suspension turrets..of course as you'll know you can also jump at the battery too..I do hope this helps..
Many thanks for rating..much appreciated..just to let you know i sent a request to close your other question you requested me with..just so you dont get charged twice.. However if you ever need to ask anything else or need advice then just ask for me and i'll get to you as soon as i can..best of luck Robert