Just got myself 8 AAs (Rechargeable) from IKEA for my custom 9,6 V battery pack which I use for my Nikko Super Cruiser. A bit overkill when you count the capacity lol. :
Nikko Toy Vehicle Accessories | Mercari
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Make your own RC Car Battery Pack or Repair NIKKO Ni-Cd 6.0V-620mAh - YouTube
Nikko 6.0V Ni-Cd Battery Pack Quick Slot Charger 4 Hour Toy RC Radio Control | eBay