[TonyM]

You must buy a generator with an inverter built in. This gives you the sine wave output which is needed for anything electronic e.g. chargers. If you use a generator without an inverter you get a rough square'ish wave output and these are fine for power tools but can easilly damage the equipment we have.

Honda suitcase inverter generators are the best, but are very expensive. Kipor is a copycat of the Honda at about half the price. I have a Kipor 2600 and it has been fine for almost three years. If I bought one again I would go for the slightly smaller/lighter 2000 model. Still plenty enough for racing use.

EDIT - here is the wording from Kipor as to why you should use an inverter generator:-
High quality power output is achieved with Kipor Generators by a built-in pure sine wave inverter, which filters the initial power of the alternator to minimise wave distortion and voltage fluctuation. This results in the output being more refined, clean and smooth. The inverter delivers a true Sine wave, no power spikes, surges or fluctuations of voltage, making it suitable for highly sensitive electronic equipment such as computers and laptops.