Video batteries do not last long. Twenty minutes recording is a usual maximum. Conserve power where possible, and make sure that you charge enough batteries for the session.
The power adapter is generally used to charge batteries. Check the instruction manual for details. Nickel-cadmium (NiCad) batteries should be stored discharged, and recharged before use. They should always be discharged fully before recharging, or they may lose their full capacity. Lead-acid batteries should be recharged after use, and stored charged.