The number of batteries needed for a skoolie conversion varies depending on the size and power requirements of the electrical system. A typical small to medium sized skoolie might need 4-6 deep cycle batteries, while a larger bus or one with more extensive electrical needs could require 8-10 batteries. The key is to determine the amp hours (Ah) required for your particular setup and then choose batteries that can provide that much power. Most lead acid deep cycle batteries are rated at around 100 Ah, so four of them would theoretically be able to provide 400 Ah of power. However, it's always best to overestimate your needs and have some extra capacity on hand, just in case.