I have a MagicShine 1400 and it was awesome up-until I read about the recall/battery probs. in the GeoMan announcement.
I swear, a day after, the light would not work.
I asked GeoMan what the 'symptoms' of a bad bat were in that thread with no response of yet, so I thought I'd throw it out here.

When the battery is plugged into the head-unit, no indicator lights on the switch - nor does it come on.
When plugged into the charger, the 'charge' LED lights green.

It took a bit to find my multi-meter ( I haven't need it since my move) I get the the following readings:
- Light-head R @ connector: ~ 1300MΩ - but then fluctuates rapidly - (I'm not sure if you can really test this...I just know it's not open - at least not to the meter...there certainly could be an open somewhere)
- Battery V @ connector: 8.45V

Seems like the batt is good to me....anyone care to probe theirs?