Cellular batteries are lithium ion or alkaline with a nominal voltage of around 3 volts and are usually labelled either by their size or shape, such as AA, AAA, C and D cell types for example; button cells batteries are often concealed forms of battery which could be in the form of watch back ups for example which might not adhere to these sizing specifications.
Button batteries are usually very small cylindrical in shape and are around the size of a coin. A typical button cell battery is LR1130 type which has dimensions of 1.6mm x 12.5mm (or 0.06in x 0.49in). The weight of this battery type is around 3g (0.11oz).