🔋 When you’re building a solar system, sizing a power bank, or choosing a backup battery for your gadgets — understanding battery capacity is key.
This guide will explain what battery capacity means, how to calculate it, and how to convert between units like Ah, mAh, and Wh — with a calculator to make it all easy.
Table of Contents
🙋 What Is Battery Capacity?
Battery capacity tells you how much energy a battery can store and deliver over time. It’s usually expressed in:
- Amp-hours (Ah) or Milliamp-hours (mAh) – common for small electronics
- Watt-hours (Wh) – used for total energy storage (power × time)
🧮 Formula 1: Convert Ah or mAh to Wh
To calculate how much energy a battery holds in watt-hours, use:
Watt-hours (Wh) = Amp-hours (Ah) × Voltage (V)If your battery capacity is in mAh (milliamps), convert it to Ah first:
Ah = mAh ÷ 1000🧮 Formula 2: Estimate How Long a Battery Will Last
Battery Life (hours) = Capacity (Wh) ÷ Load Power (W)⚡ Example
You have a 12V battery rated at 100Ah.
Wh = 100 × 12 = 1200 WhSo it stores 1200 watt-hours of energy.
If you’re powering a 100-watt device:
Battery Life = 1200 ÷ 100 = 12 hours🔋 Common Battery Examples
| Battery Type | Typical Capacity |
|---|---|
| AA (alkaline) | ~2,500 mAh |
| Smartphone battery | ~3,000–5,000 mAh |
| 12V car battery | ~50–100 Ah |
| Power bank (portable) | ~10,000 mAh |
| Home battery (Tesla) | ~13.5 kWh |
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