...
This is an optional, yet highly recommended step. One of the biggest components of M-Link is the ability to take a mirror image of the DME in its current state for safekeeping and later restoration. Since removing the DME with the battery being plugged in has the passability to set off some temporary error codes (DTCs), we recommend the user unplug his battery negative terminal before touching the DME connectors. Depending on the vehicle and configurations, there might be 1 one or two batteries present. The main one is always in the trunk and the second one (on select models such as G20), will be present under the good, on the passenger side towards the windshield.
...