I have recently got my hands on Ni-Zn batteries, which can be considered a compromise between standard alkaline batteries and the Ni-Mh rechargeable batteries. Long story short, they can be recharged and still offer a LOT of power. I was able to get 10 KM/H out of my modded 42124 with Ni-Zn batteries compared to 7 KM/H with standard alkaline Duracell batteries. More details: