Get it to the guy you bought it from, and ask him to either repair it or provide a replacement.
I had the same experience as yours, when the unit would start flashing "BATT" and then would restart. It seems the Zoom adaptor is not good enough to provide the required amount of amperage.
I am now running it on a 9V 1300mA adapter. And the problem is gone. But I would not advise this to you straightaway as it could fry the processor. I took it to a shop where we started from 9V and 500 mA and gradually moved the current up to where the issue was no more.
Also, its worth mentioning here that the sound quality improved drastically with the use of the new adaptor. There was some hiss, which was not audible initially. But when it was gone, I could make it out that it existed.
As i said, do not push 2 amperes of current down its throat straightaway. Try to first get it repaired by the person you bought it from.
My gear, currently up for sale
Washburn X-16 anarchy - SOLD!!
duncan pickups - I wonder why Im selling these.