X2 won't start except when plugged in

[mroberts]

Hi,
this may be referenced elsewhere but I couldn't see it.
Having left a couple of X2's without using them for a few weeks, they would not start up, the info keys would start to fire up and then go back to clock. The batteries were charged up with no effect. If the segways were plugeed into the charging cables then they would start up immediately (and then do the judder until the cable was unplugged). If they were switched off, then they would not start up unless plugged in. If left powered up in balance mode for an hour or so then they could be started again without plugging into mains, but the problem was back the next day when they would not start up unless plugged into the mains.
Help, please!

thanks, Martyn