1. What do you need to charge?

Pick every type you own. This is the most important filter - chemistries can't be mixed in the wrong charger.

AA / AAA rechargeables (NiMH)

C / D / 9V (NiMH)

18650 / 21700 etc. (Li-ion)

2. How many at once?

Cheap chargers often force you to charge in pairs - we only recommend independent-slot chargers.

Just 1-2

Up to 4

A lot (8+)

3. What matters most to you?

Pick up to two.

Cheap & simple

See voltage / status on a screen

Measure true capacity (find dead cells)

Charge fast

Maximum battery lifespan

Size Chemistry

Battery	Size	Chemistry	Capacity	Cycles	~$/cell	$ / 100 units*	Best for

* Value = price per 100 capacity units (mAh for NiMH, mWh for Li-ion). Lower is cheaper energy - but remember cycle life: a cell that lasts 4× longer is cheaper over its life even if pricier upfront. Capacities/prices are approximate 2026 figures.

🔋 Energy - mAh ↔ Wh

Convert capacity to energy. Wh = mAh × Volts ÷ 1000.

Capacity

mAh

Nominal voltage

Energy

2.40 Wh

⏱️ Runtime estimator

How long a cell powers a device. Uses ~85% usable efficiency.

Battery capacity

mAh

Device current draw

Estimated runtime

11.3 hours

🔌 Charge time estimator

Rough NiMH charge time. Includes ~1.4× charging inefficiency.

Battery capacity

mAh

Charger current (per slot)

Approx. charge time

2.8 hours

🧱 Pack builder (series / parallel)

Configure cells into a pack. Series adds voltage; parallel adds capacity.

Single cell

VmAh

Series (S) × Parallel (P)

Voltage

11.1 V

Capacity

6000 mAh

Energy

66.6 Wh

Uses 6 cells total.

Estimates These are planning approximations. Real runtime, charge time, and pack behaviour depend on temperature, discharge rate, cell age, and charger behaviour. Building lithium packs requires a proper BMS and safety knowledge - don't wing it.