Cylindrical Cells

A 14500 Li-ion cell measures 14mm in diameter and 50mm in length -- the same physical size as a standard AA battery -- but delivers 3.7V nominal rather than an AA's 1.5V. Because it fits mechanically into AA-sized battery holders, mixing it up with a real AA can destroy 1.5V-only circuitry.

An 18650 Li-ion cell measures 18.6mm in diameter and 65.2mm in length. It operates at 3.6V/3.7V nominal, charges up to 4.2V max, and has a discharge cutoff of 2.5V with capacities between 2200 and 3500 mAh.

A 21700 Li-ion cell measures 21.1mm in diameter and 70.4mm in length. Offering 4000 to 5000 mAh capacity at 3.6V nominal, it provides up to 50% more energy density than an 18650 cell.

A 26650 Li-ion cell measures 26mm in diameter and 65mm in length, used in high-drain devices like flashlights, power tools, and RC-hobby battery packs. The format is produced in multiple chemistries with different nominal voltages, so '26650' alone does not guarantee a specific voltage.

A 9V battery (IEC designation 6LR61, commonly called PP3) is a rectangular battery measuring approximately 48.5mm x 26.5mm x 17.5mm with two snap terminals. Alkaline 9V cells output 9.0V nominal from six internal 1.5V cells in series, with typical capacity around 400-600 mAh.

A standard AA battery measures 14.5mm in diameter and 50.5mm in length. Primary Alkaline cells output 1.5V, NiMH rechargeable cells output 1.2V. Inserting a 3.6V 14500 Li-ion cell into 1.5V AA devices destroys the circuit.

A AAA battery (IEC designation LR03, ANSI 24A) measures 10.5mm in diameter and 44.5mm in length. Alkaline AAA cells output 1.5V nominal; NiMH rechargeable AAA cells output 1.2V. Typical alkaline capacity runs roughly 800 to 1,200 mAh depending on discharge rate.

A AAAA battery (IEC designation LR8D425) is a 1.5V Alkaline cell measuring approximately 8.3mm in diameter and 42.5mm in length -- smaller than a AAA. It's used in devices with especially tight internal space, such as laser pointers, some styluses, and compact LED penlights.

A C battery (IEC designation LR14, ANSI 14A) measures 26.2mm in diameter and 50.0mm in length. Alkaline C cells output 1.5V nominal, with typical capacity in the range of roughly 6,000 to 8,000 mAh -- well above AA or AAA but less common in modern consumer electronics.

A D battery (IEC designation LR20, ANSI 13A) measures 34.2mm in diameter and 61.5mm in length -- the largest common cylindrical primary cell. Alkaline D cells output 1.5V nominal, with typical capacity in the range of roughly 12,000 to 20,000 mAh depending on discharge rate.

An N battery (IEC designation LR1) is a 1.5V Alkaline cylindrical cell measuring approximately 12.0mm in diameter and 30.2mm in length -- between a AAA and a AA in size. It was historically common in pagers and remains used in some medical devices and specialty flashlights.