Battery Efficiency Reference
Understanding efficiency losses at every stage of a battery system. From cell chemistry to inverter output, every conversion step loses energy.
Round-Trip Efficiency by Chemistry
Round-trip efficiency measures how much energy comes out of the battery compared to what went in during charging. The difference is lost as heat due to internal resistance and chemical inefficiencies.
| Chemistry | Round-Trip Efficiency | Loss per Cycle | Notes |
|---|---|---|---|
| LiFePO4 | 95–98% | 2–5% | Best available — minimal heat loss |
| NMC (Lithium) | 92–96% | 4–8% | Very good — slightly higher internal resistance |
| AGM (Sealed Lead-Acid) | 80–85% | 15–20% | Moderate — significant heat generation |
| Flooded Lead-Acid | 70–80% | 20–30% | Lowest — Peukert effect compounds losses |
Efficiency measured at 25°C at 0.5C rate. Actual efficiency varies with temperature, C-rate, and battery age.
Inverter Efficiency Ratings
Inverters convert DC battery power to AC for household loads. The efficiency rating describes how much DC energy is converted to useful AC energy. Modern pure sine wave inverters typically achieve 88–95% efficiency at rated load.
| Inverter Type | Efficiency Range | Best For |
|---|---|---|
| Pure Sine Wave | 90–95% | Sensitive electronics, medical devices |
| Modified Sine Wave | 85–90% | Basic loads, tools, lighting |
| Hybrid Inverter | 92–97% | Solar + battery systems |
Inverter efficiency varies with load. At 20% load, efficiency may drop to 80–85%. At 50–80% load, efficiency peaks at 90–95%. At full load, efficiency drops slightly due to thermal losses. Size your inverter so typical loads fall in the 30–70% range for best efficiency.
Total System Efficiency
A complete battery system has efficiency losses at every stage: charge controller, battery, inverter, and wiring. Total system efficiency is the product of all individual efficiencies.
| Component | Typical Efficiency | Notes |
|---|---|---|
| Solar Charge Controller (MPPT) | 95–98% | MPPT slightly better than PWM |
| Battery (LiFePO4) | 95–98% | Round-trip efficiency |
| Inverter (Pure Sine) | 90–95% | Varies with load level |
| Wiring Losses | 97–99% | Depends on wire gauge and length |
| Total System (LFP + MPPT + Inverter) | 78–90% | Product of all component efficiencies |
For a typical LiFePO4 system with MPPT charge controller and pure sine inverter, total system efficiency is approximately 80–88%. This means for every 1,000Wh of solar energy captured, approximately 800–880Wh reaches your AC loads.
Common Mistakes
Ignoring Inverter Losses
A 1,000W AC load requires 1,050–1,111W from the battery at 90–95% inverter efficiency. Ignoring this 5–15% overhead means the battery drains faster than calculated.
Assuming 100% Battery Efficiency
No battery is 100% efficient. Lead-acid batteries lose 15–30% of input energy as heat during charge and discharge. Even LiFePO4 loses 2–5%. Always factor round-trip efficiency into calculations.
Ignoring Wiring Losses
Long cable runs with undersized wire cause significant voltage drop and power loss. A 3% voltage drop means 3% of your energy is wasted as heat in the cables. Use proper wire gauges.
Oversizing the Inverter
An oversized inverter operating at 10–20% load has significantly lower efficiency than one operating at 50–70% load. Match inverter size to your typical load range for best efficiency.
Try It
Use the Runtime Calculator with efficiency factored in for accurate discharge duration estimates.
Open Runtime CalculatorFrequently Asked Questions
What is round-trip efficiency?
Round-trip efficiency is the percentage of energy that can be retrieved from a battery compared to the energy put in during charging. A battery with 90% round-trip efficiency loses 10% of input energy as heat during the charge-discharge cycle. LiFePO4 typically achieves 95–98% round-trip efficiency.
Why does inverter efficiency matter?
Inverters convert DC battery power to AC for household loads. This conversion is not 100% efficient — typically 85–95%. A 1,000W AC load requires 1,050–1,175W from the battery. Inverter efficiency must be factored into all runtime and sizing calculations.
How does temperature affect battery efficiency?
Cold temperatures increase internal resistance, which reduces both charge and discharge efficiency. At 0°C, a lithium battery may lose 5–10% efficiency compared to 25°C. At high temperatures, efficiency improves slightly but calendar aging accelerates.
Which battery chemistry has the best efficiency?
LiFePO4 has the highest round-trip efficiency at 95–98%. NMC lithium-ion achieves 92–96%. AGM lead-acid reaches 80–85%. Flooded lead-acid is typically 70–80%. Higher efficiency means more usable energy from the same battery capacity.