Battery Sizes

The cells a hobby project actually meets, drawn side-on to the same scale idea, with real dimensions and honest capacities instead of packaging poetry.

Name	Also called	Size	Voltage	Typical capacity	Chemistry	Lives in
AAA	LR03 / R03 / micro	10.5 × 44.5 mm	1.5 V	~1,000 mAh	alkaline	remotes, small toys
AA	LR6 / R6 / mignon	14.5 × 50.5 mm	1.5 V	~2,500 mAh	alkaline	everything since 1907
AA NiMH	HR6	14.5 × 50.5 mm	1.2 V	~2,000 mAh	NiMH rechargeable	anything that eats alkalines
C	LR14 / R14 / baby	26.2 × 50 mm	1.5 V	~8,000 mAh	alkaline	lanterns, big toys
D	LR20 / R20 / mono	34.2 × 61.5 mm	1.5 V	~12,000 mAh	alkaline	boomboxes, emergency radios
9V	PP3 / 6LR61 / E-block	26.5 × 48.5 mm	9 V	~550 mAh	alkaline	multimeters, smoke alarms
N	LR1 / E90	12 × 30.2 mm	1.5 V	~800 mAh	alkaline	small remotes, medical devices
A23	MN21 / 8LR932	10.3 × 28.5 mm	12 V	~55 mAh	stacked alkaline	garage remotes, alarm fobs
A27	MN27 / 8LR732	8 × 28.2 mm	12 V	~22 mAh	stacked alkaline	car fobs, small remotes
CR2032	coin cell	20 × 3.2 mm	3 V	~220 mAh	lithium coin	motherboards, key fobs
CR2025	coin cell	20 × 2.5 mm	3 V	~165 mAh	lithium coin	thin fobs, scales
CR2016	coin cell	20 × 1.6 mm	3 V	~90 mAh	lithium coin	watches, calculators
CR1220	coin cell	12.5 × 2 mm	3 V	~40 mAh	lithium coin	watches, small RTCs
CR123A	CR17345	17 × 34.5 mm	3 V	~1,500 mAh	lithium	cameras, tactical lights
LR44	AG13 / A76 / 357	11.6 × 5.4 mm	1.5 V	~150 mAh	alkaline button	toys, laser pointers, calipers
CR2450	coin cell	24.5 × 5 mm	3 V	~600 mAh	lithium coin	sensors, car keys
18650	Li-ion cell	18.6 × 65.2 mm	3.7 V	2,500 to 3,500 mAh	Li-ion	flashlights, power banks, packs
21700	Li-ion cell	21.7 × 70.2 mm	3.7 V	4,000 to 5,000 mAh	Li-ion	EVs, newer power tools
14500	Li-ion, AA size	14.2 × 50.2 mm	3.7 V	~800 mAh	Li-ion	flashlights, NOT an AA swap
26650	Li-ion cell	26.2 × 65.4 mm	3.7 V	~5,000 mAh	Li-ion	high-drain lights, packs
16340	RCR123A	16 × 34.5 mm	3.7 V	~700 mAh	Li-ion	rechargeable CR123A slots
Pouch	varies by cell	varies	3.7 V	100 to 10,000 mAh	Li-poly or Li-ion	drones, wearables, IoT

The numbers that deserve suspicion

Alkaline capacity is measured at tiny currents. Ask an AA for half an amp and you will see far less than the rated 2,500 mAh. A 9V is six tiny cells in a trench coat and hates real current. And any 18650 advertised above 3,600 mAh is lying, because physics has not approved more yet. Work out what your project actually gets in the battery life calculator.

Reading the lithium numbers

Cylindrical lithium cells are named by size: an 18650 is 18 mm across and 65.0 mm long, a 21700 is 21 by 70.0, and a 14500 is AA-shaped but 3.7 V, which is why dropping one into a 1.5 V device ends badly. The final digit is a zero meaning "cylinder", not a measurement.

Voltage matters more than shape

Three cells look interchangeable and are not: an alkaline AA at 1.5 V, a NiMH AA at 1.2 V, and a 14500 at 3.7 V all drop into the same holder. Some devices tolerate the NiMH, almost none survive the lithium. Check voltage before size, every time.

Handling lithium safely

Coin cells, 18650s and LiPo pouches all store real energy. Never short them, never charge a non-rechargeable, and give every rechargeable a proper protection or charger board. Swollen pouches and dented cylinders get retired, not repaired. Keep loose coin cells away from children, since swallowing one is a medical emergency rather than a scare story.