The wallmart battery's capacity is 5,200 mah (5.2 ah) -- this one lists its capacity as 39Wh (watt/hours?) -- any idea of whether one has a greater capacity?
Also, the wallmart battery's charger puts out 12v (and the charging regulator is built into the battery). Would be pretty easy to rig up a cigarette lighter adaptor to charge the wallmart battery if that's needed.