Thanks for the feedback meckyr! The more bots are connected to your battery, the higher the rate at which the battery is drained.
The charging station charges you at a fixed rate so it could be that the rate that you are being drained is higher than the rate at which you are charged.
Maybe when you stepped out, it broke the connection with some of the bots, allowing you to be charged again. Otherwise, you might have found a bug ; ;