RC Plane Lab · Field tools
Estimate how many LiPo recharges your field battery or power station can provide, with an allowance for reserve capacity and charging losses.
For standard LiPo packs refilled to 100%. Check charger and output-port power limits separately.
Field-Charging Calculator
Use the source’s rated watt-hours, or calculate them from its nominal voltage and amp-hours. The prefilled values are an example setup.
Enter your setup and select Estimate Field Recharges.
Enable JavaScript to use the calculator. The worked examples and formulas below can also be used by hand.
A complete recharge means going from your entered remaining charge to full. The result does not include flights from packs you charged at home.
Energy and power are separate checks. Watt-hours help answer “How many recharges?” Watts help answer “Can this outlet and charger support my charging setup?” A good energy result does not verify electrical compatibility.
Worked examples: how much field-charging energy do you need?
These are calculated examples, not product tests. Each starts with a full source, leaves a 20% source reserve, uses an 80% energy-transfer assumption, and refills each flight pack from 20% to full.
| Source | Flight pack | Energy per refill | Complete recharges |
|---|---|---|---|
| 500 Wh | 3S 2,200 mAh | 19.5 Wh | 16 |
| 500 Wh | 4S 5,000 mAh | 59.2 Wh | 5 |
| 500 Wh | 6S 5,000 mAh | 88.8 Wh | 3 |
| 12.8 V, 40 Ah (512 Wh) | 6S 5,000 mAh | 88.8 Wh | 3 |
For the 500 Wh source, the model allocates 500 × 0.80 × 0.80 = 320 Wh to the flight packs. A 6S 5,000 mAh pack has a nominal energy of 6 × 3.7 × 5 = 111 Wh. Replacing 80% of that is approximately 88.8 Wh. Divide 320 by 88.8: about 3.60 recharge equivalents, or three complete refills with energy left for a partial fourth.
Six of those refills require about 532.8 Wh delivered to the packs. With the same reserve and loss assumptions, the modeled source rating is 532.8 ÷ 0.80 ÷ 0.80 = 832.5 Wh. Treat that as a planning threshold; uncertainty and other loads require additional room.
Change the energy-transfer assumption to 70%, and that six-refill source estimate rises to about 951.4 Wh. At 90%, it falls to 740 Wh. Those are sensitivity examples, not a promise that your setup operates within that range.
Check the output port, charger, and charge rate
A large battery does not guarantee a high-power outlet. Check these limits separately before choosing equipment or increasing a charge setting:
- Source output: use the continuous rating of the specific AC or DC port you will connect to. Shared port limits and the source battery’s current limit also matter.
- Charger input: confirm AC/DC compatibility, input-voltage range, input-current limits, and any reduced power available at lower input voltages.
- Charger output: check total wattage, wattage per channel, maximum current, supported chemistry, and cell count.
- Battery and wiring: use a charge rate permitted by the pack manufacturer, correct polarity and connectors, and appropriately rated wiring and protection.
For a standard 6S 5,000 mAh LiPo, a 1C setting is 5 A. Near its 25.2 V full-charge voltage, supporting 5 A calls for about 126 W at the charger output; the input must provide more because the charger has losses. Current tapers near the end of a normal charge. This power calculation is not permission to charge a particular pack at 1C. SkyRC explains the same voltage, current, and charger-wattage relationship.
As a concrete port example, the EcoFlow DELTA 3 Plus manual lists 1,024 Wh of stored energy but a shared 126 W limit for its 12 V DC outputs. That DC limit leaves insufficient input power to sustain a full 126 W of charger output after losses. This illustrates a specification check, not a product recommendation.
A compatible DC charging path may avoid the inverter stage used by an AC charger. Check the actual voltage and port limits before assuming it is the better choice. For charge-rate and channel selection, use our RC battery charger guide. To estimate the wait between flights, open the LiPo charge-time calculator.
How the calculator works
It uses nominal energy as a practical approximation. Goal Zero’s explanation of watt-hours describes the distinction between energy and power and the nominal-voltage × amp-hours conversion.
Source energy (Wh) = rated Wh, or nominal source volts × source Ah
Source fraction available = (starting charge % − reserve %) ÷ 100
Energy per refill (Wh) ≈ cells × 3.7 × (pack mAh ÷ 1,000) × (100 − remaining %) ÷ 100
Energy reaching packs (Wh) ≈ source Wh × available fraction × transfer factor
Complete recharges = energy reaching packs ÷ energy per refill, rounded down
Source rating for your target (Wh) ≈ target recharges × energy per refill ÷ available fraction ÷ transfer factor
What can make the real result different?
The model treats the entered charge percentages as proportional to nominal energy. Real battery voltage changes during use and charging; percentage displays are estimates. Capacity varies with battery age, temperature, load, and cutoff settings. Charger losses and inverter overhead also change with operating conditions.
The 20% source reserve and 80% transfer factor are example inputs. They are not validated defaults for every lithium, lead-acid, or power-station battery. Choose a reserve compatible with your source’s permitted discharge limits; an older source may also need a lower effective capacity input.
Cooling fans, phones, lights, and inverter idle time can consume energy between charges. They are not separately modeled here. Budget for them and compare the prediction with a measured session before relying on it for a full flying day. Do not add solar-panel nameplate watts directly to battery watt-hours; solar contribution depends on energy actually collected over time.
For a mixed fleet, calculate the refill energy for each pack size, multiply by the number of those refills, and add the results. Then apply the same source reserve and charging-loss allowance to that combined energy need. Do not add the separate “complete recharge” counts from one source.
Make the estimate fit your flying routine
Start by counting the recharges you need after arrival. Bring fully charged packs into that plan separately. Two packs recharged together still consume the energy of two refills; multiple charger channels mainly change how you schedule the work.
Record pack size, capacity returned by the charger, completed refills, source charge before and after the session, and any other loads. Compare repeated sessions under similar conditions. A charger’s mAh counter measures returned charge, not watt-hours; use the nominal-voltage conversion only as an approximation. An energy meter at the charger input excludes upstream inverter or source losses, so do not mistake that reading for an end-to-end efficiency measurement.
Balance-charge with the correct chemistry and cell count, keep charging attended on a suitable nonflammable surface, let hot flight packs cool, and stop using damaged packs. Keep the source and charger within their specified temperature and ventilation limits. See the LiPo charging, storage, and care guide and your equipment manuals.