The Math of Survival: Calculating Runtimes for Your Ecarke DeWALT Power Station

You bought the Ecarke 200W Inverter. You have a stack of yellow DeWALT batteries. Now the power is out, and you need to know: How long will this keep my laptop running?

Most people guess. Engineers calculate. The beauty of using tool batteries for backup power is their predictability. Unlike a gas generator that runs until the tank is dry (a variable amount of time depending on load), a lithium battery is a finite bucket of energy. By understanding the math of Watt-Hours (Wh), you can plan your emergency strategy with precision.

This guide moves beyond the “it works” reviews to give you the operational data you need to trust this device in a blackout or at a campsite.

The Energy Bucket: Ah vs. Wh

DeWALT markets batteries by Voltage (V) and Amp-Hours (Ah). * Voltage: 20V (Max) / 18V (Nominal). For calculation, we use 18V. * Amp-Hours: The capacity. 2Ah, 5Ah, 6Ah, etc.

To compare this to your devices, you need Watt-Hours (Wh).
Formula: $Wh = V \times Ah$

Common DeWALT Battery Capacities

• Compact (2Ah): $18V \times 2Ah = \mathbf{36Wh}$. (Tiny. Good for one phone charge).
• Standard XR (5Ah): $18V \times 5Ah = \mathbf{90Wh}$. (The workhorse).
• High Output (6Ah/8Ah): $18V \times 8Ah = \mathbf{144Wh}$. (CPAP territory).
• FlexVolt (9Ah/12Ah): $18V \times 12Ah = \mathbf{216Wh}$. (Serious power).

Note: Even though FlexVolt is 60V, it switches to 20V parallel mode when plugged into a 20V tool/inverter, so the Wh math stays consistent.

The Efficiency Tax: The 85% Rule

You never get 100% of the energy out.
1. Inverter Loss: Converting DC to AC creates heat. The Ecarke is roughly 85% efficient.
2. Depth of Discharge (DOD): The LVP (Low Voltage Protection) cuts off before the battery is chemically empty to save it. You get about 95% of the rated capacity.

Realistic Wh = Rated Wh x 0.85 (Efficiency) x 0.95 (DOD) Rated Wh x 0.8 * Safe Rule of Thumb: You have 80% of the sticker capacity available for your device.

Scenario 1: The CPAP User (Brandon’s Case)

User Brandon Crone used an 8Ah battery for his CPAP. * Total Energy: $144Wh \times 0.8 = \mathbf{115Wh}$ usable. * CPAP Load: A standard CPAP (without humidifier heater) draws about 30-40 Watts. * Runtime: $115Wh / 35W \approx \mathbf{3.3 \text{ Hours}}$.

Wait, Brandon said “through the night.”
The Nuance: CPAP machines don’t draw constant power. They draw power based on your breathing pressure. The average draw is often much lower, perhaps 15-20W if the pressure is low and the heater is off. * Revised Runtime: $115Wh / 15W = \mathbf{7.6 \text{ Hours}}$.
Verdict: An 8Ah battery is the minimum for a full night’s sleep. A 5Ah battery (72 usable Wh) would die around 3-4 AM. If you use a heated hose, you need a FlexVolt 12Ah or multiple batteries.

Scenario 2: The Remote Worker (Laptop)

A typical modern laptop (e.g., MacBook Air) has a 50Wh battery. * The 5Ah Battery (90Wh):
* Usable: ~72Wh.
* Result: You can fully recharge your laptop 1.4 times. * The Workflow: If your laptop lasts 6 hours on its own, a single 5Ah DeWALT battery extends your workday to 14+ hours. * USB-C vs AC: User wilson noted the presence of a USB-C port. If your laptop charges via USB-C, USE IT.
* AC Path: DC(Batt) -> AC(Inv) -> DC(Laptop Brick) -> Battery. Double conversion loss (~70% efficiency).
* USB-C Path: DC(Batt) -> DC(USB) -> Battery. Single conversion (~90% efficiency).
* Using the USB-C port gives you an extra hour of runtime purely by skipping the AC conversion.

Scenario 3: The Light Tower

The Ecarke has a built-in 200lm LED light. * Draw: 200 lumens is roughly 2-3 Watts for LED. * Runtime on 5Ah: $72Wh / 3W = \mathbf{24 \text{ Hours}}$. * Tactical Use: In a blackout, don’t use the inverter for lights. Use the built-in LED. It runs for days. If you need room lighting, plug a low-wattage LED lamp (5W-9W) into the AC outlet. A 5Ah battery can light a room for 2 nights easily.

The Heat Warning: Continuous Load

Just because it can output 200W doesn’t mean it should continuously. * 200W Load: Drains a 5Ah battery in 20 minutes. * Thermal Throttling: At 200W, the plastic casing will get hot. The internal fan will scream. * Recommendation: Keep continuous loads under 100W. Use the 200W headroom for startup surges (like a laptop brick plugging in) but don’t try to run a 150W gaming PC or a TV for hours. It’s a sprinter, not a marathon runner at high loads.

Verdict: The Distributed Microgrid

The true power of the Ecarke isn’t just one unit. It’s the ability to buy three or four of them for the price of one Jackery.
If you have 4 DeWALT batteries, buying 4 inverters ($200 total) gives you four independent power stations. * One for the CPAP in the bedroom. * One for the Wi-Fi router in the hall. * One for the laptop in the office. * One for charging phones in the kitchen.
This Distributed Microgrid is far more resilient than a single large generator. If one fails, you still have three. For the prepared homeowner, this modularity is the ultimate advantage.