Battery Life Calculator
Calculate estimated battery runtime accounting for Peukert's Law and discharge depth.
About
Estimating how long a battery will last is rarely as simple as dividing capacity by load. As discharge rate increases, the effective capacity of a lead-acid battery decreases - a phenomenon known as the Peukert Effect. This calculator provides a more realistic runtime estimation by factoring in the battery's chemistry and discharge rate.
Accurate battery sizing is critical for off-grid solar systems, UPS backups, and electric vehicles. Underestimating the load can lead to premature shutdown, while failing to account for Depth of Discharge (DoD) limits can permanently damage battery cells. This tool helps engineers and hobbyists predict safe operational windows.
Formulas
The modified Peukert's formula determines time t (hours) based on rated capacity C (Amp-hours), load current I (Amps), and the Peukert constant k:
Where H is the rated discharge time (usually 20 hours for lead-acid). For simple approximations (or Lithium where k ≈ 1), the basic formula is used:
Reference Data
| Chemistry | Peukert Constant (k) | Typical DoD Limit | Application |
|---|---|---|---|
| AGM Lead Acid | 1.05 - 1.15 | 50% | UPS, Solar Backup |
| Flooded Lead Acid | 1.20 - 1.40 | 50% | Golf Carts, Marine |
| Gel Lead Acid | 1.10 - 1.25 | 50% | Deep Cycle Solar |
| Lithium (LiFePO4) | 1.01 - 1.05 | 80-90% | EVs, Modern Solar |
| NiMH | 1.20 | 80% | Consumer Electronics |