Why get a generator ? It's noisy, polluting and expensive. We use old car batteries and it works fine, just have to be careful with the acid. With a 16A battery you can charge up to 15 3300's, so there's plenty of power, and if you are afraid of being short in power, just bring two.
Besides, kufman's calculation is wrong, it's 5A charge at 7.2V (theoretically, in practice the mean is closer to 8V) not 12V, which makes a slight difference.