The voltage needed depends on the internal resistance of the battery which increases with charge, that is why when charging a battery the amperage decreases as the battery is charged. There is a huge difference from delivering 5 amps to delivering 90 amps, you would need 18 times the voltage, 5 amps is easy and cheap. The best power supply I got delivers up to 50 amps @ up to 20 volts DC continuous and it is not cheap.
It is possible that the gadget works though, battery chemistry is complex and people are alway coming up with new ways of improving cycle life of not only lead batteries but also NiCads and other types.

Jl