1st: I tried to perform a search to see if this was covered already, but we all know how pathetic the search function is on this forum.
2nd: I tried to use Google but BMWMOA forum links were broken.
OK, so I don't use my car specific Garmin 40LM on my motorcycle, but with this unit having a built-in Lithium-Ion battery, the issue I had may apply to the Zumo and other similar models.
I started having short battery life and was about to order a new battery for this unit. But with it being about 18 months old and having worked in a defense lab with batteries and battery chargers, I knew the battery issue I was having was not the norm.
So I contacted Garmin; great service as usual by the way.
This is the response that I got and the instructions that I followed that worked. Note: leave the GPS connected for the duration recommended. It is a slow process.
Thank you for contacting Garmin International.
I am happy to assist you. It sounds like your device needs to be reset. Please turn the device on without any power connected to it. Once you do this please allow the device to completely drain of all battery. At this point please follow the instructions below. This should reset the battery so it will take a complete charge. Please advise.
Please plug your device into the computer and press and hold the power button for 8-10 seconds. The device may not power on immediately. Please allow the device to charge on the computer for a full 8-12 hours. Please be sure that the computer does not time out or have a screensaver come on. This can cut off power to the device and it will not charge. Once the charge has completed I recommend updating the operating system software. Please follow the link below for instructions. Please be sure to do all of the additional updates except for the voices you do not speak, the help files, and the vehicles. Please let us know if you have any further questions.