I'd backup Wendelspanwick's concerns regarding cordless tools. I have some ten or so tools from the Makita 18 volt range and while I think they are very excellent indeed, I am well aware of their limitations in terms of running time especially when under heavy load - particularly in my case the chainsaw (BUC122Z) and the circular saw (BSS610Z).
I've also seen how much battery capability deteriorates with usage over time - that is the batteries I have which date from the time of buying my first tools maybe 6-7 years ago have now been used and charged so many times that they provide only a small amount of use in some tools before a noticeable drop in power/performance. I bought four new batteries towards the end of last year (I stick with genuine Makita ones) giving me a total of eight, all labelled so I know which are the newer ones. The older ones are still OK for use in the Makita torch for example or for jobs where I'm only using the tool for a few minutes. Continued use of the older batteries will I hope extend the life of the newer ones, using those only when necessary. I have successfully charged batteries when away from the mains using an inverter and a 12-volt power source such as leisure batteries. A pure sine wave inverter is I think needed to operate the Makita charger properly. With a tool such as the chainsaw though you can easily exhaust batteries quicker than they can be recharged. If you already have cordless tools (as I had), you might be able to make it work for you, but if starting out, I'd look at corded ones.
I recently bought a generator (http://www.thegreenreaper.co.uk/Generators/Petrol_Generators/Briggs_and_Stratton_Pro_Max_3500A_Long_Run_Petrol_Generator_3.4KVA.html) which I'm very pleased with. Note the voltage regulation feature which means it should be able to drive anything upto the power rating including items with 'sensitive' electronics (such as the Makita charger for instance). Note also the headline rating of 3.4kVA, not to be confused with the maximum wattage of the items it can power (2700). My best tip for generator use is a long cable so you can site the (noisy) generator away from where you're working. This one by the way adequately drives my 2200 watt electric log splitter.