Replacement from Amazon
You can still buy GenZe batteries for $435 plus shipping.
My original battery lasted 3 or 4 years.
I Paid almost $500 to have it rebuilt, which lasted about a year.
This time I bought a 36v battery on Amazon for $119. Opened the original battery on both ends, removed the batteries and circuit board (slides out easily), cut the wires, connected the two power wires from the end that goes into the bottom of the battery slot.
The pack I bought didn't fit in the slot, so I velcroed it to the bike.
Seems to work well so far.