This was happening to our machine. After inspecting the battery I discovered that the 'clip' on the bottom of the battery was stuck in the casing, there is a release button beside that clip, Press it in and the clip will pop out.
I believe that clip holds the battery in place. I'm not sure but suspect that is a safety feature to diconnect the battery if the motor heats up after you tangled the roller in the rug tassles. We had the same issue and it fixed the problem