I now have my Evader scooter powered by two YESA 48V, 20AH LiFePo4 packs wired in parallel, and I have run them through about 20 charging cycles to date. I am charging them with a Taiwan made 48V, 8A SLA charger I purchased on Ebay and all seems fine(the slighly lower charging voltage will probably extend the life of the batteries somewhat). Today I rode 25 miles and still had power left to go a few more miles. The parallel arrangement seems to work well (I am charging and discharging in parallel), and I expect even more range when it warms up here in Rochester, NY (it was 50F today when I rode).
I have had a good experience with YESA but not with the shipping of these packs from China. The first pack came through with the package damaged and one of the cells dented, but it still worked ok. The second pack came through with the package damaged and one of the cells shorted out. YESA quickly sent me a free replacement cell, but I had to pay for shipping. I consider this fair treatment under the circumstances. Replacing the bad cell turned out to be pretty easy.
FYI, the Evader is a 48V large scooter which came originally with 48V, 40AH of SLA's. Replacing the SLA's with the LiFePo4 packs reduced the weight of the scooter by about 100 lbs. The exchange went off pretty easily but the Evader doesn't use a voltage converter to get 12V for the accessories. Instead it simply grabs 12V off of one of the SLA's, so I had to tap off one of the LiFePo4 packs 4 cells into the pack to get the 12V I needed. Top speed is about 32 mph. I expect that range will be above 30 miles when the temperature here rises to 80F or so.