You can only start the fan and pump when it's charging and i usually do.
I also use a big fan to blow past the battery. Not very focussed. But again, i allready had it, it uses 60W so the generator doesn't mind.
And again, very minimal affect if any but also very cheap. If you don't run dirty enviroments: Cut or drill the rear part of the front fender. More air flow over the battery and more towards the cooling and fan.