Charger Wattage & Charging Time
Estimate how long a phone, laptop or power bank takes to charge from its battery size and charger wattage, free online.
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Charging time ≈ battery energy (Wh) ÷ (charger power × efficiency). Battery Wh = mAh × voltage ÷ 1000 (a 5000 mAh phone cell at 3.85 V is 19.3 Wh). Charging slows above ~80% to protect the battery, so the last 20% takes a similar time to the first 80% on fast chargers.