Garmin e Trex - E Plug question

[ThomTom]

I use a Garmin e Trex and need to find a 12 volt chrages to use on the bike.  it stil uses a stupid plug called an ePlug.  Idealy I want to convert the unit to 12 volt and have someone just solder the conections inside the unit.  I have no need to use it of the bike.  Any suggestions??