hi
will depend on how much racing your gonna do in a day and in what rc type youre racing . if you only get 3 heats and a final you may make it without recharging lipos (you should be able to get two runs out of a large capacity lipo without emptying it
off road 4wd will be more draining than 2wd and touring cars tend to be less thirsty than off road
many clubs have mains facilities available some do not . I always take a leisure battery everywhere just in case
try a tyre/ battery centre they often have batteries they want rid of (not good enough for car but plenty good enough for a days racing . you get one for a few beer tokens
hope this helps dave