I myself have found a issue on two different picocalc boards where plugging USB into the pico will apply that power directly to the batteries and overcharge them. I have also seen it happen to someone on discord, but he had no clue it was overcharged (his orange charge light had the fast “danger” flash when he plugged USB into his picocalc).
I had been in communication with Alex, but his reply was a bit vague on whether or not they confirmed the problem existed. I had asked them to put out an official warning, but it seems they haven’t done so ¯\_(ツ)_/¯
Therefore, consider this an unofficial warning from some random internet stranger: Do not plug power into pi pico (or your module of choice) while picocalc is powered on and batteries are installed. Doing so can overcharge them to dangerous levels.