Answer:
When the battery is almost fully charged.
Step-by-step explanation:
A battery is a term used to describe any device that has the capability to convert chemical energy through an oxidation-reduction(redox) reaction taking place within the electrical circuit.
A battery usually have two ends, named as a cathode electrode(Positive) and an anode(negative) electrode. Batteries usually give off the most gas when they are almost fully charged, that is while it is advisable not to over charge a battery.