Battery Life Calculator
Calculate battery runtime from capacity and load current. Essential for device selection and power planning.
Battery Runtime Calculation
How to Calculate Battery Life
Simple formula: Runtime = Capacity ÷ Current. A 5000mAh power bank charging a phone at 500mA lasts about 10 hours in theory. In practice? 7-8 hours. You lose 20-30% to heat and conversion inefficiency. Always assume real-world will be shorter.
Temperature matters hugely. Cold cuts capacity. Heat kills lifespan. That power bank in the car in summer? Way shorter runtime. Old batteries hold way less charge than new ones too.
Battery Rating Types (And What They Mean)
- Amp-Hours (Ah): A 100 Ah battery can do 1A for 100 hours (theoretically). More useful for larger batteries.
- Milliamp-Hours (mAh): Phones and power banks. 5000 mAh = 5 Ah. Your phone is probably 3000-4500 mAh.
- Watt-Hours (Wh): The real measure. Independent of voltage. Wh = Ah × Voltage. Two batteries with same mAh but different voltages have different energy.
What Actually Eats Your Battery
Cold weather kills available capacity—a battery that's 100% at room temp might be 70% at freezing. Heat permanently damages it. Variable loads drain faster than steady ones. Converters lose 10-20% as heat. Older batteries naturally hold less. Budget conservatively.
Common Batteries and Reality
| Battery Type | What You Get | Where It Lives | How Long It Lasts |
|---|---|---|---|
| Alkaline AA/AAA | 1.5-2.8 Ah @ 1.5V | Remotes, flashlights | 5-10 years on shelf |
| Lithium-Ion (Li-Po) | 2000-5000 mAh | Phones, laptops, drones | 2-3 years or 500-1000 charges |
| Lithium Iron Phosphate | 100-200 Ah | Solar, RVs, EVs | 10+ years, 3000-5000 charges |
| Lead-Acid (AGM) | 50-200 Ah | Cars, UPS, boats | 3-5 years, 300-1000 charges |
| Nickel-Metal Hydride | 1.2-2.5 Ah | Rechargeable AAs | 3-5 years, 1000 charges |
Actually Keeping Your Battery Alive
Keep it cool (not hot, and not freezing). Don't fully drain it (stop at 20%). Use the right charger. Watch for swelling. Clean the contacts. For your phone: dim the screen, turn off Bluetooth when you don't need it. Every little bit helps.
