Haha. I just searched google and found this place. I'm an electrical engineer and just started fixing my mothers Think (Th!nk) bike by ford. We gave her the bike as a gift back in 2002 or so. Awhile back the bike stopped working (battery would not charge) and it sat for some time. Anyway, I literally just started working on it today (6-16-2009).
If the bike is not used for some time (over about 6-8 weeks, maybe less if the batteries are old), the battery voltage becomes too low. When the voltage is too low, the "smart" charger determines the batteries to be shorted or not connected. Thus it looks like the charger and/or battery does not work.
To fix this problem, the batteries voltages need to be increases to a point where the charger can recognize them again. Once the batteries are recognized, the bike well function like new. There are two ways to get the voltage up in the batteries:
1. (Best). Unscrew the battery case. It opens up easily. It holds two motorcycle batteries. I found two of these inside my think battery:
(I'm not allowed to post links)I can assume the yuasa batteries have been discontinued, as I can not find one. I found this replacement:
(cant post links check batterymart)
This replacement battery is actually better (more range) then the stock battery. YOU NEED TO ORDER TWO. Changing these is easier then changing a car battery. They fit inside the stock think battery case and operate exactly like the stock batteries (same charger, ect). btw- the battery case has a built in de-sulfate.
2. Semi-charge the batteries manually. You can use a car 12v battery charger, but it must NOT be a smart charger (ie: auto shut down, auto fault protection, no safety features). You could charge it off a car battery too. You don't need a 24v charger, because you are only putting enough voltage in the batteries for the think charger to recognize the battery again and fully recharge it. Anything near the 14v range should be plenty for the OEM think charger to detect the battery.
Hope this helps!!!