Battery Replacement
The first indication of a failing battery is (not-surprisingly) slow cranking. My 730 has done this for a year now and so I decided to replace it before it expired suddenly, which tends to be how things go. It seems batteries that are installed away from the hot engine compartment last a long time - this BMW-branded example lasted about seven years, assuming it wasn't the original from 1991 as we have no record of a replacement being fitted. When I found one of the (+) cables carelessly caught and squished under the battery I knew immediately that our local dealer did the job before selling us the car in 1998.
I bought a Hella Endurant based on precise local knowledge, namely that "everything else is rubbish." It's a DIN85 size and looks exactly like the OEM battery. I was told that the "L" suffix refers to the terminal arrangement is no longer used as it is the default.
Be careful that the cables are clear before you clamp it down. And, plug in the external vent tube at the (+) end which passes combustible fumes to the outside and check that the opposite end is plugged. I would also suggest cleaning the terminals and clamps with one of those clever wire brushes designed for the purpose.