Rechargeable Batteries.

[wildwood]

Is there a reason why the common rechargeable batteries only employ 1.2volts? Some gadgets need a full 1.5v.(or 3v.)

[Old_Geezer]

It's to do with how they're made, which chemicals are used in the construction. One can't dictate on nature what pd will appear across the junction, just take what develops and use it to form batteries. For most purposes the tolerance between different types is not significant. If a gadget can't cope with rechargable batteries then IMO they were not well designed.

[BRIGHT SPARK]

The maximum voltage obtainable from a CELL is 1.2v. A battery is the name given to a group of cells generally wired in series to obtain a higher voltage.

[beso]

Cell voltage is not limited to 1.2 volts but as OG said it depends on the chemistry of the technology.

The nominal cell voltage for a Carbon Zinc battery is 1.5 volts while for Nickel Cadmium and Nickel Metal Hydride rechargables it is 1.2 volts.

Consequently some devices designed for C-Zn are not able to run on rechargable batteries because the voltage is too low.

Lithium Ion batteries have a nominal voltage of 3.7 volts so they are not produced in the A, C or D formats.