Electric Dirt Bike FOR KIDS

For the kids dirt bike,the current battery capacity is 36V 4Ah,some customer feedback the battery capacity is not enough,how do you think of it?do you also think need to enlarge the battery capacity?

Item: Electric Dirt Bike

Battery: 36V 4.0Ah Lithium Battery

Plastic: Environmental PP

Motor: 36V*Brushless*350W Aluminim

Brake: Aluminum handle brake

Wheel: 12 inch Inflatable off road 

Suspension: High-elastic front and

                       rear shock absorbers

Range:11-15KM

Max Speed:15-18-25km/h

Charging Time:3-5hrs

Age:6+

Max Loading: 85KGS

Size: 110*60*73CM