Calculator Inputs
Formula Used
This calculator estimates usable battery energy, then divides by average load.
- Nominal Wh = V × Ah (or use entered Wh)
- Usable Wh = Nominal Wh × DoD × Efficiency × Health × TempFactor
- Avg Power = (V × AvgCurrent) × DutyCycle or (AvgPower × DutyCycle)
- Runtime (hours) = Usable Wh ÷ Avg Power
- Runtime (minutes) = Runtime (hours) × 60
How to Use
- Enter your battery voltage and either Ah or Wh.
- Set depth of discharge and efficiency for realism.
- Choose current or power, then enter your average load.
- Adjust duty cycle to match garden work pauses.
- Press calculate and download CSV or PDF if needed.
Example Data Table
| Scenario | Battery | Load | Duty | Usable Wh | Runtime (min) |
|---|---|---|---|---|---|
| Raised bed screws | 18V, 5Ah | 4.5A avg | 45% | ~60 Wh | ~44 |
| Pilot holes in cedar | 18V, 2Ah | 120W avg | 60% | ~24 Wh | ~20 |
| Soil mixing with auger | 20V, 6Ah | 180W avg | 70% | ~75 Wh | ~36 |
Examples are illustrative. Your drill, bit, and material change load.
Practical Notes
Battery energy and what it really means
Most cordless drill packs advertise voltage and amp-hours, but runtime depends on watt-hours. Watt-hours equal voltage multiplied by capacity, so an 18V 5Ah pack stores about 90Wh. This calculator applies depth of discharge, efficiency, battery health, and temperature to estimate usable watt-hours for gardening projects. If your pack lists both Ah and Wh, prefer Wh because brands sometimes quote nominal voltage differently across platforms.
Load varies by task, bit, and material
Average load changes dramatically between light fastening and heavy drilling. Screwing into soft pine can draw only a few amps, while large spade bits, hole saws, or soil augers can push power much higher. Using the duty cycle input helps model real work patterns with pauses, alignment, and repositioning. Base input on the toughest step always.
Efficiency and settings that extend runtime
Mechanical and electrical losses mean the tool never converts battery energy perfectly into work. Lower torque settings, sharp bits, and pilot holes reduce resistance and lower average power. For repetitive garden assembly, switching to a lower speed range and steady pressure often reduces stalls and saves battery energy.
Temperature and battery age effects
Cool mornings can reduce available energy, while hot afternoons can increase internal resistance and heat the pack under load. Older batteries also lose capacity and deliver shorter sessions. The health and temperature factors let you build realistic expectations, especially when planning long garden builds away from charging access. When batteries feel hot, let them rest; cooler packs deliver steadier voltage under the same demand.
Planning swaps and spares for smooth workflow
Use the minutes estimate to schedule breaks and battery swaps before performance drops. For example, if the tool estimates 35 minutes at your chosen duty cycle, plan a swap around 25–30 minutes. Carrying a second pack keeps productivity steady, especially during fence repairs, raised-bed builds, and trellis installations. Log a few runs in the CSV export to build a personal baseline for each task and battery.
FAQs
Should I enter Ah or Wh?
Enter Ah if you know the pack’s capacity and voltage. Enter Wh if it’s printed on the label. When Wh is provided, it overrides the voltage × Ah calculation for a cleaner estimate.
What duty cycle should I use for garden work?
Light fastening often fits 30–50%. Mixed drilling and fastening is commonly 50–70%. Heavy drilling or augers may be 70–90% when you are continuously working without many pauses.
Why does efficiency matter so much?
Some energy becomes heat in the motor, electronics, and gearbox. Lower efficiency reduces usable energy for work. A realistic efficiency range for many tools is 80–90%, depending on load and condition.
How do I estimate average current or power?
If you have a clamp meter, measure current during typical work, then average it. Otherwise, use a conservative power guess based on your task and adjust until the runtime estimate matches your experience.
Why is my real runtime shorter than the estimate?
High torque spikes, dull bits, deep holes, and hard materials raise power draw. Battery protection may also cut off earlier under heavy load. Lower the duty cycle or raise average power to model this behavior.
Can I compare two batteries with different voltages?
Yes. Compare usable watt-hours and the resulting minutes at the same average power. Higher voltage packs may run cooler at the same power, but watt-hours remain the most direct energy comparison.