Is that the current voltage, or when new? Do you know the chemistry or cell configuration? That is an oddball number. Maybe LifePo4? Standard Lithium 10S "36V" battery should be 42.0, fully charged when new.

If you are interested in dealing with an honest and reputable vendor, I would suggest Paul (Cellman) at Em3Ev. Do some research, I have. Certain companies I would not recommend under any circumstances.

Pay special attention to both output and charging connectors, I would also recommend one of the newer variable chargers that can charge to 80, 90, or 100% so that the battery can be stored at a lower charge level and last significantly longer, though 6 years is a long time in battery years no matter what you do.