30-second summary
Alkaline vs. Rechargeable – Voltage
In practice, alkaline batteries and rechargeable batteries can be used interchangeably in sets. They have only different voltage characteristics. It is given by their different chemistry. Primary cells gradually drop in voltage from use. They start at 1.5 volts, drop to 1.2 and continue to 1.0 where the appliance stops working. Secondary cells operate more uniformly, even with only 1.2 volts. They have flat discharge where they pretty much stay at 1.2 volts until depleted and then drop off very quickly to below 1.0 volts.
The overall reaction for the alkaline battery:
Zn(s) + 2MnO2(s) ⇌ ZnO(s) + Mn2O3(s) [e° = +1.43 V]
The overall reaction for the NiMH battery:
NiO(OH) + MH → Ni(OH)2 + M [e° = +1.32 V]
An alkaline battery (IEC code: L) is a type of primary battery that provides direct electric current from the electrochemical reaction between zinc and manganese dioxide (MnO2) in the presence of an alkaline electrolyte.
The alkaline battery gets its name because it has an alkaline electrolyte of potassium hydroxide (KOH) instead of the acidic ammonium chloride (NH4Cl) or zinc chloride (ZnCl2) electrolyte of the zinc–carbon batteries. Other battery systems also use alkaline electrolytes, but they use different active materials for the electrodes.
The primary alkaline battery is a widely used product, which is essential for powering many portable devices, such as power tools, radios, toys, and remote controls. The most common size of alkaline battery is the well-known AA battery. Alkaline batteries are most commonly used in portable devices that have low current drains, are used only intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available.
Why are alkaline batteries (AAA or AA) made to be 1.5V while rechargeables are 1.2V?
In general, batteries convert stored chemical energy into electrical energy through an electrochemical process. This then provides a source of electromotive force to enable currents to flow in electric and electronic circuits.
- Primary (single-use or alkaline) batteries use cells that have 1.5V open circuit voltage when fresh.
- Secondary (rechargeable) batteries use cells from NiMh or NiCd, which have 1.2V open circuit voltage.
In practice, alkaline batteries and rechargeable batteries can be used interchangeably in sets. They have only different voltage characteristics. It is given by their different chemistry. Primary cells gradually drop in voltage from use. They start at 1.5 volts, drop to 1.2 and continue to 1.0 where the appliance stops working. Secondary cells operate more uniformly, even with only 1.2 volts. They have flat discharge where they pretty much stay at 1.2 volts until depleted and then drop off very quickly to below 1.0 volts.
Since electronic devices are usually made to run from cell voltages of 1.0 to 1.5 volts, alkaline batteries and rechargeable batteries perform similarly. In fact, it’s generally considered that secondary 1.2 V cells work better than alkalines having lower output impedance and more consistent voltage from start to finish of a charge.
