Razor has already stuffed the largest size batteries that could possibly fit inside of the E300 scooter's battery box so to modify the scooter to have larger batteries would require raising the footplate. Two 12V 15Ah batteries will fit in the battery box and stick up around 1-1/2" above the frame.
Two 12V 12Ah or 12V 15Ah Batteries
Two 12V 10Ah Batteries
Please let us know if you have any questions.
The extra ride time with a larger battery pack will be between proportional to over-proportional to the increase in the battery pack's Ah rating. For example, if the original 7Ah batteries provide a 40 minute ride time then 14Ah batteries would provide a ride time between 80 and 88 minutes depending on the conditions that the scooter is driven under.