Know when pruners, lights, and sensors recharge fully. Adjust for efficiency, heat, and battery limits. Pick the best charger and get back outside faster.
Use this for garden tools, sensors, lights, timers, and power banks. It supports partial charges, charger losses, optional solar variability, and charging while the device is running.
| Garden device | Battery | Charger | Efficiency | Charge window | Estimated time |
|---|---|---|---|---|---|
| Cordless pruner battery | 2000 mAh @ 18 V (36 Wh) | 42 W charger | 85% | 20% -> 90% | ≈ 0:48 |
| Garden sensor pack | 3000 mAh @ 3.7 V (11.1 Wh) | 10 W USB | 80% | 10% -> 100% | ≈ 1:35 |
| Headlamp | 1500 mAh @ 3.7 V (5.6 Wh) | 5 W USB | 85% | 30% -> 100% | ≈ 0:57 |
| Watering timer | 2500 mAh @ 3.7 V (9.3 Wh) | 7.5 W USB | 80% | 40% -> 95% | ≈ 1:01 |
| Handheld sprayer | 5000 mAh @ 7.4 V (37 Wh) | 30 W adapter | 85% | 0% -> 80% | ≈ 1:27 |
1) Convert battery capacity to energy (Wh)
If you enter mAh and voltage: Wh = (mAh / 1000) * V
If you enter Wh directly, that value is used.
2) Energy needed for the chosen charge window
EnergyNeeded(Wh) = BatteryWhFull * (Target% - Start%) / 100
3) Effective charging power
Charger power is adjusted by efficiency, temperature derating, and solar variability:
UsablePower(W) = ChargerPower * Eff * (1 - TempDerate) * (1 - SolarVar)
4) Net power and time
If the device consumes power while charging:
NetPower(W) = UsablePower - DeviceLoad
Time(hours) = EnergyNeeded / NetPower
5) Optional top-off taper
Charging slows near full; when enabled, extra time is added above 80%.
Charging time depends on battery energy, not just a charger label. This calculator converts your battery rating into watt-hours, then scales it to the refill you want, such as 20% to 90%. Use it for cordless pruners, sensor hubs, headlamps, sprayers, and portable lights. If your battery lists watt-hours, enter it directly. If it lists mAh, add nominal voltage for accurate conversion.
Not all charger power reaches the cells. Cable resistance, adapter heat, and conversion stages reduce usable power, so the efficiency field models that loss. Temperature derating reflects protective limits that slow charging when packs get warm. For solar chargers, variability represents fluctuating input power from clouds or panel angle. These adjustments turn nameplate watts into an effective charging rate.
Full charges often take longer because the final portion fills slowly. Set a target below 100% when you need tools ready sooner, and enable top-off taper when charging above 80%. This helps you compare a quick recharge to finish today’s tasks versus a longer session that maximizes runtime tomorrow.
In the garden, devices may draw power during charging, such as work lights, irrigation controllers, or monitoring stations. Add that load to estimate net charging power. When device load approaches effective charger output, charging can stall or drain the battery. The warning notes help you choose a stronger adapter or turn features off.
Repeatable maintenance improves reliability. Export results to CSV for logging battery health, charger performance, and seasonal patterns. Use PDF for a printable checklist for staff, workshops, or tool cabinets. Records make it easier to replace aging packs, upgrade a charger, or adjust routines for hot weather. Use the cost fields to estimate energy expense per recharge, helpful when running charging stations off-grid generators or shared workshop outlets during busy spring peak seasons.
Start with 80–90% for USB and adapters. Use 70–80% for older cables or multi-stage conversions. If your measured charge time is longer than estimated, lower efficiency until it matches reality.
Multiply amp-hours by nominal voltage. The calculator does this automatically: Wh = (mAh ÷ 1000) × V. Use 3.7 V for single-cell Li-ion, or the pack’s labeled voltage for tools.
Most batteries use a constant-current, then constant-voltage phase. As the pack approaches full, current tapers down to protect the cells. Enable the top-off taper option when targeting above 80%.
Yes. Enter the device load in watts to subtract it from effective charger power. If load is close to charger output, charging may stall. Reduce load or upgrade the charger for a positive net rate.
Enter your charger’s rated power, then add solar variability to reflect clouds and panel angle. For stable midday sun, 5–15% works. For shifting shade or winter sun, try 25–50%.
They export your inputs, computed power values, energy added, and estimated time in both hours and hh:mm format. Use CSV for logging and comparisons, and PDF for printing or sharing with a team.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.