The battery tap is usually a white or black balancing plug that comes off your battery that you plug into your charger when you have a battery with multiple cells in series (if you don’t know what series is, go to our “what does series mean?” FAQ). If you have multiple cells in series you need to keep those cells in balance to maximize performance and cycle life, meaning they need to all have the same voltage when the charging process is finished. If a battery gets out of balance, one cell in the pack can get charged too much while another cell can get discharged too much. That balancing tap is there to make sure all of your cells stay within close voltage range when charging and discharging your battery.