Every charge–discharge cycle loses energy to heat and BMS overhead. This battery round-trip efficiency calculator converts energy in and energy out in watt-hours into round-trip efficiency % for solar storage and off-grid planning.
Benefits
- Core formula: efficiency % = (Wh out ÷ Wh in) × 100.
- Quantifies one full charge-to-usable-discharge cycle.
- Benchmarks real packs against 95%+ Li vs. 80–85% lead-acid norms.
How it works
- Log energy in (Wh) from charger or solar into the bank for one cycle.
- Log energy out (Wh) delivered to loads before the next recharge.
- Read round-trip efficiency %—loss is 100% minus efficiency.
FAQ
What is battery round-trip efficiency?
It is usable energy out divided by energy stored in, × 100, for one cycle. Example: 1,000 Wh in, 950 Wh out → 95% round-trip efficiency. The missing 50 Wh became heat, BMS draw, and internal resistance loss.
How do I measure Wh in and Wh out?
Use a battery monitor shunt, inverter cumulative kWh, or charger meter. Wh in is what the pack accepted during charge; Wh out is what loads consumed from that charge window—before the next top-up.
What is a good round-trip efficiency?
Modern lithium often tests 93–98% at moderate C-rates; lead-acid may land 80–88% depending on age and charge profile. Compare your measured % to datasheet values at similar charge amps and depth of discharge.
Technical specifications
- Round-trip efficiency % = (energy_out_Wh ÷ energy_in_Wh) × 100.
- Loss Wh = energy_in − energy_out.
- Output Wh cannot exceed input Wh in passive systems.
- Related: battery-efficiency, battery-charging-time, battery-energy.