Battery size generally refers to the shape, voltage, and terminal layout of a battery. Thus the term "size" has become interchangeable with "type". Batteries of different types will usually not have the same dimensions and terminal layout.
Here are some examples:
AA - The normal voltage output of an AA battery is the same as an AAA battery, C cell or D cell; AA batteries, however, provide power for a longer period than AAA batteries, hence their larger size, and for less time than C or D batteries, which themselves are larger than AA cells. An AA cell measures 51 mm long, 15 mm in diameter, and weighs approximately 23 g (1.97 x 0.56 inches and 0.81 ounces).
Penlight
MignonLR6 (alkaline)
R6 (carbon-zinc)
FR6 (Lithium-FeS2)
KR157/51 (NiCd)15A (alkaline)
15D (carbon-zinc)
15LF (Lithium-FeS2)
10015 (NiCd)
1.2H2 (NiMH)2700 (alkaline)
1100 (carbon-zinc)
3000 (Lithium-FeS2)
600-1000 (NiCd)
1700-2900 (NiMH)1.5
1.2 (NiCd)
1.2 (NiMH)Cylinder+ Nub cylinder end
- Flat opposite endL 51 mm
D 15 mmC7/HP7;
AAA
Microlight
PotloodLR3 (alkaline)
R3 (carbon-zinc)24A (alkaline)
24D (carbon-zinc)1200 (alkaline)
540 (carbon-zinc)
800-1000 (Ni-MH)1.5
1.2 (NiCd)
1.2 (NiMH)Cylinder+ Nub cylinder end
- Flat opposite endL 44.5 mm
D 10.5 mmC16/HP16;
http://en.wikipedia.org/wiki/List_of_battery_sizes