Ah to Wh Cell-Format Gallery

The first dry cell - the Leclanche zinc-carbon cell - was patented by Georges Leclanche in 1866. It produced ~ 1.5 V and was the ancestor of the AA, AAA, C, and D formats. The size standards we use today were defined by ANSI in 1924 (D was the first), AA in 1947, AAA in 1959, and 9V (which is six tiny cylindrical cells inside a brick) in 1956 by Eveready specifically for transistor radios. The Wh capacities of these formats have improved roughly 3x since 1924 through chemistry refinements but their physical dimensions and nominal voltages are fixed by the original specs - astonishing standardisation that has outlasted vacuum tubes.

Alkaline chemistry, introduced by Lewis Urry at Eveready in 1959, replaced zinc-carbon as the dominant primary chemistry by the 1980s. Alkaline cells deliver higher Ah (especially at high drains), lower self-discharge, and a flatter discharge voltage curve. The same 1.5 V open-circuit voltage as zinc-carbon, but with 2-3x the energy density. A modern Duracell AA holds 2.85 Ah = 4.275 Wh at low draw. The chemistry has been incrementally refined since 1959 but the fundamentals are unchanged.

Coin cells (CR2032 and siblings) entered the consumer market in 1971 via Panasonic. The chemistry is lithium-manganese-dioxide: 3.0 V open circuit, extremely low self-discharge (~ 1 percent/year), and a tiny package that suits motherboard CMOS, keyfobs, hearing aids, and medical implants. The CR2032 specifically (20 mm diameter, 3.2 mm thick, 220 mAh) was standardised in 1989 and is the most widely manufactured coin cell in the world - several billion sold per year. Its 25-year-on-CMOS lifespan is the canonical example of microwatt-class power budgeting.

Lithium-ion arrived in 1991 when Sony shipped the first commercial 18650 cell in a CCD-TR1 Handycam camcorder. The 3.6 V nominal voltage and 1500 mAh initial capacity were both unprecedented. By 1996 the 18650 was the standard laptop cell; by 2008 Tesla had built the Roadster pack from 6831 of them. Modern 18650 cells deliver up to 3500 mAh in the same can - a 2.3x improvement in 35 years driven by silicon-doped anodes, dry-coated electrodes, and tighter manufacturing tolerances. Production now tops 15 billion 18650 cells per year worldwide.

The 21700 format (21 mm x 70 mm) was introduced by Tesla and Panasonic in 2017 for the Model 3 / Model Y battery packs. The roughly 50 percent volume increase over 18650 translates to roughly 50 percent more energy per cell (~ 18.5 Wh vs ~ 12 Wh). More importantly, fewer cells per pack means lower BMS overhead, fewer interconnections, and easier thermal management. Power tools (Milwaukee M18 HD, DeWalt FlexVolt) and high-end electric bicycles adopted 21700 by 2019, making it the new mainstream high-power cell.

Lead-acid car batteries have changed remarkably little since 1920. A modern 70 Ah SLI starter battery uses the same 12.6 V nominal voltage (six 2.1 V cells in series) as a 1920 Buick. The lead grids are now thinner (better surface area), the electrolyte is sometimes gelled (AGM) for spill-proofing, but the chemistry is identical. Lead-acid's 30 Wh/kg energy density is laughable compared to lithium's 250 Wh/kg, but lead is recyclable at 99 percent rate, dirt cheap, and tolerant of abuse - which is why every ICE car still has one even when the rest of the electronics has gone lithium.

Forklift batteries are the unsung giants of industrial electrochemistry. A typical 48 V 800 Ah pack contains 24 large 2 V flooded lead-acid cells weighing ~ 60 kg each - 1500 kg total. The same cells that powered streetcars in the 1890s, just bigger. They deliver 80 A continuous for an 8-hour shift and survive 1500 cycles in warehouse use. Lithium replacements (LFP) exist but cost 4x more per kWh and are only displacing lead in cold-storage warehouses where lead-acid performs poorly. Lead-acid in forklifts will persist for another 20 years simply on economics.