The dry cell (Leclanché cell) comprises of a zinc case and graphite rod, separated by a paste of MnO2, NH4Cl and carbon.
Oxidation of zinc:
Zn(s) => Zn2+(aq) + 2e-
Reduction of manganese:
NH4+(aq) + MnO2(s) + H2O(l) + e– → Mn(OH)3(s) + NH3(aq)
at the carbon rod where manganese is reduced from an oxidation state of +4 to +3. This cell initially has a voltage of 1.5V which gradually decreases as the cell is used.
In the button cell (silver oxide cell) zinc is also the anode:
Zn(s) + 2OH–(aq) → ZnO(s) ,,+ H2O(l ),, + 2e–
with the cathode reaction in silver oxide:
Ag2O(s) + H2O(l ) + 2e– → 2Ag(s) + 2OH–(aq)
The electrolyte solution KOH in a porous medium separates the zinc and silver oxide.
Both the dry cell and button cell are cheap and useful when small currents are needed for a long time. They are small and easily portable. The button cell delivers a very constant voltage throughout its lifetime as there is no change in the concentration of KOH, while the dry cell has a relatively short shell life of around 1.5 years, as the zinc is attacked by ammonium chloride paste which is acidic.
As the first commercial battery, the dry cell was the first commercial battery and therefore had a significant impact on society, making possible things such as flashlights and portable radios. The button cell allowed for miniature electrical appliances such as watches, and since is it non toxic it can be used inside the body.
The dry cell and button cell are both primary cells, ie they are non-rechargeable and have to be disposed. However, neither have toxic materials and both have minimal environmental impact upon disposal.