Have the charger plugged in to the wall, then plug balance lead into charger. Sometimes I have to plug in and remove the balance plug several times, then the green light will start It can take up to 3 hours to charge, and make sure robot is off.

Everything is plugged in. The green light flashed when I initially plug it in then goes out.

Did you use the battery pack right before trying to charge it? It shouldn't take a charge till it cools off.

I don't think the battery was warm, but I'll let it sit for a while.

I would suggest something similar to Steve, sometimes the balance connector from the battery doesn't make good contact to the charger so unplugging it and plugging it back it a couple times usually does the trick to get the green light to turn on.

I have tried plugging it in many times. Is it possible that I need a new battery or charger?

It sounds like you have done all the troubleshooting, so If it is not charging the battery, then I would say yes, you do need a new charger. Has the charger ever worked since you got it? Is it the charger that came with Roli, if not where did you get the charger from? And how long have you had it for? Maybe you could get a replacement under warrenty if you havn't had it very long, as it does sound faulty.

It's possible, it depends how low you let the battery get...

Can you measure the voltage of the battery? There are a few ways to do that.

1. The balance plug (outside 2 pins)
2. The micro deans connector on the back of the robot (remove the EZ-B to access it)
3. With the EZ-B turned on, across any Vcc (red) and Ground (black) pins.

If the battery has gone under voltage it will refuse to accept a charge. It should not go under voltage since the EZ-B warns of low battery well above the under volt level but it may be worth checking.