The battery version commonly used tubes where the filament was heated by a single 1.5-volt dry cell and plate voltage was supplied by a (nominally) 90-volt battery.
Unlike a wet cell, a dry cell can operate in any orientation without spilling, as it contains no free liquid, making it suitable for portable equipment.
Conveniently manufactured, and disposed, a single zinccarbon dry cell has low environmental impact on disposal, compared with some other battery types.