The Compass tricycle is prepared/wired up to accept a second battery if desired. It ships with what seems to be two batteries, however, the right one is an empty case. The left battery is the viable one. When using the tricycle make sure the power switch (on the left battery) on the tricycle is switched on.
Installing the second battery simply requires the unlocking and removal of the empty case and sliding in the second battery. Lock both batteries in place before riding. The Compass will automatically switch to the second battery when the charge on the first is depleted. Both units must be switched on for this.