An electrode includes separate first and second electrical contacts to contact the skin of a subject. A charge-holding structure is electrically connected between the first and second contacts. An indicator is operatively coupled to the charge-holding structure so that the indicator changes visibly in response to a change in the charge stored in the charge-holding structure. The electrode can include a rectifier across the contacts. A container for electrodes includes an electrical supply and a plurality of receptacles for electrodes so that a voltage difference is maintained across conductors of each receptacle (and contacts of an electrode therein) for at least one week. A method of making electrodes includes arranging the contacts over a support, connecting the charge-holding structure between them, arranging the indicator over the support, and charging the charge-holding structure so that the indicator has a first visual appearance.