[Al Skierkiewicz]

In general, using a battery charger in parallel with the battery while connected to a load, is a bad idea for the electronics that are connected as part of the load. The charger (even smart chargers) are confused by the varying load/battery combined and will on occasion produce the maximum voltage the charger is capable of generating. This condition is bad for both the electronics and battery. A high current power supply as Erik has suggested might be available from your mentoring organization but these items are rare for most businesses. You can substitute a larger battery, i.e. a automotive battery, for testing purposes if you need extended battery times. Please be sure to insulate any wiring you choose to make. With the battery disconnected from the robot, you can then charge the larger battery with an appropriate rated charger.