Question 1

How do I calculate battery life?

Accepted Answer

Battery life (hours) = capacity (Ah) ÷ device current draw (A). For example, a 2500 mAh battery powering a 250 mA device runs for about 10 hours. Account for efficiency by multiplying by 0.7-0.85 for real-world runtime.

Question 2

How do I convert mAh to Wh?

Accepted Answer

Wh = (mAh × voltage) ÷ 1000. A 3000 mAh 3.7V Li-ion cell stores about 11.1 Wh of energy. Multiply by 3.6 instead of dividing voltage by 1000 for an equivalent formula.

Question 3

What efficiency should I use?

Accepted Answer

Use 100% for an ideal estimate, 80-85% for typical DC-DC regulator losses, and 70% for older linear regulators or high-drain devices like motors and heaters.

Question 4

How long does it take to charge a battery?

Accepted Answer

Charge time = capacity ÷ charge current × 1.4 (for the typical CC/CV Li-ion charging overhead). A 2000 mAh battery at a 1000 mA charger takes about 2.8 hours to reach full.