Battery Runtime
Calculate how long a battery will last under a given load
Lead-acid: 50%; LiFePO₄: 80–100%
Lead-acid: ~1.1; LiFePO₄: ~1.05; ideal: 1.0
Runtime
Realistic runtime accounts for the Peukert effect (higher current → lower effective capacity).
How does it work?
Ideal runtime = (Ah × V × DoD) / W load. For example, 100 Ah 12 V battery, 80% DoD, 50 W load: (100 × 12 × 0.8) / 50 = 19.2 h.
Depth of discharge (DoD) limits how much of the battery you use. Lead-acid: typically 50%. LiFePO₄: 80–100%.
Peukert effect means higher discharge current reduces a lead-acid battery's effective capacity. LiFePO₄ has a Peukert exponent close to 1.0 (nearly ideal). Lead-acid: 1.1–1.3.
Example
Example: Lead-acid 100 Ah, 12 V, 100 W load, DoD 50%, Peukert 1.1.
Ideal: (100 × 12 × 0.5) / 100 = 6.0 h
Actual current: 100/12 = 8.33 A; C20 rate: 5 A
Peukert: 20 × (5/8.33)^1.1 × 0.5 ≈ 5.5 h
Assumptions
- •Constant load (variable loads not supported)
- •Peukert calculation assumes 20-hour (C20) rated capacity
- •Temperature effects on capacity are not included