Wow those batteries can output 5 AMPS of current, Anyways, they are at 1.2 volts, you would need quite a few, why don't you use a Lead Acid battery?
Say, like this one?
At 12 Amps, They should work Wonderfully, They should be able to power the arduino alone for a bit over a month. 
And charging them is very easy, use any 12 power supply with at least 1 amp of current and no more than 3 amps.
Be careful with it though, reverse polarity, and your arduino is fried, along with anything else, these batteries are serious business.