RE: towers 420 charger ?
No, not nessecarily. It will depend on the rate used. A 1C rate (capacity times 1) would be about an hour for a dead batt.
A max charge rate of 2C on the 2/3A cells will charge in half that time because the rate is doubled and that's about max for a small cell because of temperature. If your batt happens to be a 1100 nimh then a 2 amp rate is considered max and the dig piranha will go up to 3 amps. If I was in a real pinch I may charge at 3 amps, but 5 amps is too fast.