If you want a good reliable battery that isn't going to fail look at Bosch equipped bikes. I have had in total 3 Bosch batteries fail in 10 years with at least 1000 Bosch Equipped batteries sold and all of them got taken care of under warranty (save for one which was purchased second hand). Plus with Bosch you can go into most any shop that is a QBP dealer (which is most shops in this country) and get support. Bosch has some of the best customer service in the biz and really support their products well and will have parts long term so when they discontinue a motor they will usually have parts for 10-16 years after that because they know there stuff is reliable long term so they need that long term support. There are other great e-bike systems out there but Bosch is generally tops in reliability and durability and if you want a folding bike Tern makes some really excellent ones and use the Bosch system and they themselves also have great support as well.