Well, if you want a custom battery, you can always bump up the power on one of the pink batteries. They only wiegh like 8kg, and can be placed almost anywhere. I picked up a "portable nuclear reactor" by RyanRulez, and made a conversion for it into a high-powered airtank. Both parts together weighed 16kg, fit in the space of two pink batteries, and powered a SHW for quite a long time.....