There are basically two options for supplying power to astronomical mounts and other equipment: power supplies or batteries.
A power supply provides constant voltage for an unlimited period of time. It is therefore the first choice for a stationary operation in the garden, on the patio or the balcony. However, batteries are required for mobile astronomy. These are often also called powertanks.
You should not be too thrifty when buying a powertank: in cold weather, the power drops quickly and some mount "errors" are in fact due to a weak power supply.
Many smaller GoTo mounts have an integrated battery compartment. Operating such a mount via a power supply or a rechargeable battery is definitely cheaper and more environmentally friendly in the long term.