I changed mine a few years ago. I know the battery type and instructions were in a thread like this.
Found thsi that mihght help.
"I have an old Hugo that completely died. When the batteries go, you can't use the device.
Finding new ones has been almost impossible and the cost to have someone do it is ... crazy
Here's the solution
https://www.walmart.com/ip/Tenergy-...ry-Pack-w-PCB-1S1P-9-62Wh-3-5A-Rate/318401510
solder out the stock, and solder two of these... took 5 minutes! success....
be sure red to (+) and black to (-)"