ElectricScooterParts.com Support Center

From looking at the photos of your battery pack we can confirm that it is wired correctly.

New batteries should have a nearly full charge in them when shipped, however, to format them they should be charged for 12 hours before their first use. The charger in your photo is the right Voltage and Amperage for a 12Ah-15Ah battery pack. Some lead-acid batteries will make a little bit of fuzzing sound when charging while others will not. If the batteries are making a fizzing sound then we recommend keeping an eye on them for their first charge to make sure they don't start to get hot, which would indicate a problem with them. When recharging a 12Ah-15Ah battery pack with a 1.5 Amp charger we would not expect the batteries to get warm and to stay cool.

When making the final connection of the wiring harness to a switch or battery a pop or spark is normal. So long as both wires go to the switches contact leads then it should not matter which wire goes to which lead. If the motor runs at all then the power switch is wired correctly and working. The power switch cannot cause a partial loss of power problem,

The battery load test results show low Voltages so that may be what is causing the low motor power problem.  The individual batteries should be at around 13.8 Volts each when not under load, and when under a heavy load should drop around 1 Volt. 

We can not say for certain that the problem is undercharged batteries but we recommend recharging the battery pack for 12 hours and then see how the go-kart operates then.

If a 12-hour charge does not help then please let us know and we will take it from there.