after six years and less than sixty cycles my battery is on its last legs, looking for reasonably priced replacement. This is for the Trek Valencia with the ride+ system, purchased in July 2011. Any input is appreciated. Battery is 40.7 volts, 6.4 Ah, 260 Wh rated for lifetime of 600 cycles

did you check at Luna website? they make all kinds of batteries. I also wonder if Trek has any in stock? good luck.

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.

Lots of 'battery rebuild' services available, esp on eBay. You send them your battery and they open up the case and replace the individual cells inside with new ones.

You need a 42 volt battery.

Where did the 40.7 number come from? The difference between a 40.7 and a 42 volt battery is trivial. People often run 48v systems at 52, or even 36volts systems at 48.