We do build custom battery packs. The cost is structured by size of battery and complication. If the battery is built using our standard formations it is just a price for that size of battery. If the build requires some addtional production time i.e. End to end battery or custom configuration there may be a build fee. Each job is different. Give us a call toll free at 888 654 4450 and we can steer you in the right direction.