Hello, my name is***** thing with the DM5 is that it needs to be connected to another DM5 with midi to backup your data. The battery will last about 10-15 years. It's best to take it to a shop that has another DM5 to use as a backup.
If you open it up and take a look at the battery location, determine if you can switch it out while the power is plugged in. If it is plugged in and turned on, the battery can be replaced without losing data. As long as power is applied, you will not lose your data.