Batteries should last for a number of years. However, there are many variables which can affect battery life; it's important to look after your battery!

The most important thing is to never to leave your bike with a flat battery. Keep your battery hooked up to a charger so it doesn't discharge. There are lots of battery chargers out there, so it's important to make sure that you have one that is relevant to the battery fitted to your bike - most BMW's will come with lead-acid batteries but some models are starting to appear with lithium batteries which require a specific charger. If it is easy to remove the battery from your bike, you can bring it indoors and keep it on a trickle charger - also recommended if you do not have a power source where your bike is kept. Again, we carry a large range of battery chargers to cover all options. 

How do I check my battery if I think it is dead? To double check it may be worth charging it whilst disconnected from the bike; since some electrical problems on the bike could lead to a constant drain on the battery whilst the ignition is off. (i.e. leaky diodes in the charging circuit).

A faster test is to use a multi-meter between say the battery +, and the + cable (disconnected from the battery) and check there's no current flowing with the ignition off. Start with about 5A setting just in case, then work down to about 500mA (fsd).

Any current flowing over say 50mA (allowing for alarms/clock etc) suggests there may be an electrical problem other than the battery.