2000 BMW 740i starting/battery problem. Battery seems to drain when the car is not being used daily (lights get dimmer) then starter will only "click" then nothing. Boosted to start and ran for 1 hour to charge. All ok then but only for 2-3 weeks. Battery is 2 years old and expensive. Is this a battery that will charge but not hold (an electric leak?) or is it an issue with the starter? Or other? Also, noticed that as the problem develops that the length of time needed to turn the starter to get ignition increases and it sounds like it is struggling more.

Cars & Trucks - BMW - X7 Series - 2000 BMW 7 Series