... What do "M" and "G" stand for?
Where is the power supply to the charger? What are your polarities?
What does 12/115V mean? DC/AC ? Is that a convertor?
Your charger should not care how long the input or output leads are, within reason.
M stands for Motor and G for Generator. Sorry, I thought these abbreviations would be standard. You are correct 12/115V means: a converter 115V AC to 12 V DC. Also, no negative lines are shown.