I have tips for battery last longer, my current battery still in service for more than 5 years i believe. When batteriku still cheap.

1. I relocate the battery from the front to the rear. Less heat = happy battery.
2. Its a weekend car, so i remove the battery terminal when not in use, its a maintenance century free battery.

I did it myself, just need to buy.
1. clamps
2. 400 amp welding cable, but if you could get BMW battery cable, it is much better.
3. grounding cables
4. fuse 200amp.

at first i ran the welding cable trough the interior of my car, but its too tight and part of the cable was sliced by the firewall, so i remove it completely and buy another one to run it under my car and go up back trough the rear spare tire compartment. Routing was much easier, and a bit safer rather than running it inside your car. FYI grounding cable or points is twice important than the power cable. Previously i hard a crank issue where the engine was so hard to start and found out that it was due to lack of grounding.