A 4.5” X ” X 1.5” (about the same size as iPhone) polished plastic ABS box is provided that contains:
The modified Hiface is incorporated into the box.
A recommended battery charger can be permanently connected to this box & when the switch is in the off position the batteries are charged.
The LiFePO4 chargers recommended here automatically turn off when fully charged so they can be left permanently plugged in.
This is a plug & forget arrangement i.e. you don't have to think about battery operation - they will run for 6 hours continuous use before needing re-charge & will last for 15 - 20 years!
3.3V Lithium NanoPhosphate Batteries (LiFePO4)
These unique 3.3V batteries are the batteries used in electric vehicles & have a lifetime of about 15 years (in this high current use). They do not suffer memory effects & hold their 3.3- 3.2V voltage output steady until depleted. More importantly for powering clocks they seem to have very low noise.