The One uses a rechargeable Lithium Ion battery so there's no need to replace batteries. The USB-style charger cable is included, along with compact world-wide AC charger (100-240V).
The battery capacity has been designed to require only one or perhaps two charge cycles per week - see the analysis below.
Battery Level is indicated on the 0 - 10 scale allowing you to easily check remaining capacity. There are multiple warning levels, so the One will warn you well ahead of the time if you need to recharge your stethoscope.
(Note: This scale normally indicates volume.)
This chart shows an actual discharge cycle for an active One driving headphones. Battery life is more than 250 minutes of patient listening.
(Stethoscope will actually operate down to 3 Volts!)
One can estimate a typical use case as follows, if we assume 2 minutes of auscultation per patient - a rather long estimate:
Listening Time (T) =2 minutes/patient (estimate)
Battery Capacity (B) > 250 minutes
Patient Capacity (P)=B/T=125 patients
Daily Patients (Pd)=25 patients/day (estimate)
Estimated Days (D) =P/Pd=5 Day patient load