I believe it is 52 type 18650 2600 mah 3.7 volt LiPo's. 13 of these batteries in series equals 48.1 volts. Four sets of these in parallel equals 10,400 mah, or 10.4 amps. This is just my best guess based on common, inexpensive, reliable, rechargable batteries. It could be totally different, but based on the physical size of the battery packs this would work. If this is the case, you could theoretically replace them with 3500mah cells and get a 48 volt, 14,000mah or 14 amp battery pack. Again, although both size ratings are common for ebikes, I am just speculating based on my experience with rechargable cells.