My 2-9s had gauges instead of the LED, but otherwise they worked in a similar manner to my 2-31. The difference was that while the 2-31 has banana plugs and could work off of batteries, the 2-9 required timer power and had a 5-pin plug that constantly bent pins.
The big issues are the power requirements of the cell, the different wiring required, and the pinout of the wiring. You don't want to cross wires, as that tends to blow them up. Tag doesn't support them anymore, so you'd have to fix them yourself if they died. If you still have the manual it should have the required information.
Good luck.
