modality - a method of therapy that involves physical or electrical therapeutic treatment. rehabilitation - the treatment of physical disabilities by massage and electrotherapy and exercises.
Alkaline AA batteries are rated 1.5 volts, while NiMH AA batteries are rated at 1.2 volts. NiMH generally refers to a battery being rechargeable and to the materials from which the battery is constructed.
Many batteries are made of these metals, therefore they will all give off the same voltage. AA, AAA, C, and D batteries all give off 1.5V (if they are made with NiZn). The size difference accounts longer battery life, or even spreading the batteries current out over a greater distance. Now the 9 volt battery is a little bit different. In the common AA battery, there is a typically a Zinc rod, surrounded by a paste (the electrolyte, or a bridge for the electrons), the paste is contained within a Nickel tube (lets call this tube/paste/rod mixture a cell).