The above 6 No.5 dry batteries are 9V (NiMH batteries are 7.2V) and 3 18650 lithium batteries in series are 12V. The operating voltage is too high and some PCB components are easily damaged. It is recommended to use 2 18650 lithium batteries (7.4V). Since the working flow of small cars is very large (about 1A), you need to know whether your lithium battery has a protection plate and whether it can carry as much current as a small car.
Yes, the original 5 cell battery can be replaced with a 7.2 volt battery. The original 3 cell battery can be used with a 4.8 volt battery. The one pictured is a 4.8 volt battery. Open the original battery compartment and remove the original shrapnel to modify the battery interface and battery. can be easily disassembled. Then just buy an adapter sector suitable for charging the battery.