||The otoscope head can be powered by disposable dry batteries, rechargeable nickel cadmium cells or from an a.c. (mains) transformer.
The voltage required is determined solely by the characteristics of the bulb fitted to the instrument.
The power source for the otoscope should incorporate a variable rheostat to enable the examiner to adjust to optimum the brilliance and colour temperature of the light.
Whereas the voltage available from ordinary dry cells decreases consistently with use, a rechargeable nickel cadmium battery handle eliminates frequent battery changes and provides a relatively uniform voltage output almost to the end of discharge.
The most convenient of rechargeable handles plug directly into an a.c. (mains) outlet and will recharge automatically if left overnight.
Otoscope battery handles:
Left: 2.5 V battery handle for C size cells (Welch Allyn 70 500),
Right: a wall rechargeable 3.5 V handle (Welch Allyn 71000).