Battery checkThe original of this text is from Pokie Midgley, he agreed that I use his photos (which has saved me a lot of work) and translated the text into German. However, it has become a very free translation, in which I have added parts in some places or I have added a few more. Shortened.
Checking the battery acid level
BMW did not make it easy for Cruiser drivers to get the battery. For this purpose, the fuel tank, the seat and the side panels must be removed (see also the description on how to remove the tank). Nevertheless, it is necessary to check the acid level of the battery every 20000 km, at least once a year.
After removing the tank, the battery can be removed without any problems. Unscrew the negative cable first, then the positive cable. Put the nuts and bolts aside so that you can find them later. Disconnect the breather hose at the battery (do not pull the breather hose out of the bike or it will be very fiddly to re-route it). Unhook the strap holding the battery – you can then lift the battery out.
To check the level of the battery fluid, place the battery on a level surface. Take a flashlight as shown in the picture and shine it through the battery from behind. Now try to see how high the acid level is in the battery. Since this is sometimes a bit difficult to detect you may have to replace the battery or. Move the flashlight a little bit. The battery acid may be filled up to the upper mark at the most.
When reinstalling the battery, first reconnect the positive cable. At the end put some pole grease on the poles to prevent corrosion.
Refilling the battery
If there is too little fluid in the battery (i.E. Below the minimum mark) it must be topped up.
A word to the Caution: Battery acid is a dangerous liquid! So always use protection for your eyes and skin – and don't drip anything on your clothes. If battery acid gets on your skin, wash it off immediately. If battery acid splashes into your eyes, rinse your eyes immediately with LARGE amounts of water and consult an ophthalmologist. If you get battery acid on your clothes, you will find nice little holes in them after the next clothes wash … Therefore be careful when filling up the battery.
Check the battery charge level before refilling – it should be charged before refilling. For those who want to use an acid tester (simple ones are available from approx. 5 €) have: A fully charged battery has at approx. 20 degrees Celsius approx. 1,26-1,30 g/ml acid density. You can also measure the voltage. This should be more than 11.8 volts (for measurement if necessary). A small load, z.B. Connect a 12V bulb or similar). Usually the maximum charging current should not exceed 10% of the capacity. After charging, shake the battery a little so that the gas bubbles come out. So much for the theory (in practice, I have never checked or charged a battery that was able to spin the starter quickly before refilling 
To refill the battery, use distilled water only – but never overfill (not above the upper mark). If too much battery fluid is added, it will cause two problems: first, battery fluid will leak and second, since only distilled water is added, overfilling will dilute the electrolyte and weaken the battery.
To refill distilled water you have to open the filler caps on the battery. These can be removed with a small screwdriver or. The acid level of the battery can be levered out with a small pair of pliers – but be especially careful, as battery acid may spray up. To top up, it is best to use a small funnel or.