The Duke of Wirdum

Most rechargeable batteries are 1,2V= in stead of 1,5V=. With 6 batteries that adds up to 1,8V= less. That might not seem a lot but it's still 20% loss. 7.2V= volt in stead of the required 9V= 1,5V= recargable batteries do exsist but you'l have too look for them and you'l need the right charger. Plus the fact that most rechargeable batteries preforme less under load than a non-rechargeable battery. If you realy want to go rechargeable, go for the lego rechargeable battery pack.