psst.. the oade cable that powers the M1 from 6v SLA works on the JB3
same size and all. they add diodes that drop the voltage 1.2v for the M1. i just connected it to my JB3 and powers up fine and plays. the ac power plug led is lit. I havent tested a recording on it, but there shouldbt be any reason why it wouldnt be fine.
the only issue would be putting a batter connector on it for your particular brand, ie: ecocharge, home-made etc.
I will do a run-time recording test tonight with a 6v 4.5 Ah and see how long it records for successfully. if i can find some diodes, ill be happy to mod your existing cables car adapter cable along with a 4.5 aH battery
or call oade brothers and buy your own M1 cable