A 3,600mAh power bank usually delivers about 8–9Wh of usable energy—roughly one small-phone charge or 1.5–2 hours at 5–10W.
You came here to find out how far a 3,600mAh pack really goes. Short answer up top, details below. The trick is to turn that milliamp-hour label into watt-hours, then account for losses. Once you do that, you can predict screen-on time, charge counts, and whether a tiny pack will limp you through a commute or a long layover.
3600mAh Power Bank Runtime—What To Expect
Most slim packs use a single-cell lithium-ion battery with a nominal 3.7V. Energy (the fuel you can spend) is better expressed in watt-hours (Wh). Here’s the simple chain:
- Convert to Wh: 3,600mAh = 3.6Ah. Energy ≈ 3.6Ah × 3.7V = 13.3Wh.
- Account for losses: Boosting 3.7V up to 5V (or 9V/12V with fast charge), cable losses, and the device’s own charging losses eat a chunk of energy. In the real world, you’ll see about 60–70% of the label. That leaves roughly 8–9Wh usable.
Why talk in Wh at all? Because Wh maps directly to time at a given power draw (W). Power × time = energy. That’s the cleanest way to estimate hours for lights, fans, or a phone under load. (See the plain-English note on energy units from Battery University on Wh and W.)
Quick Reference: Hours From A 3,600mAh Pack
The table below assumes ~65% usable energy (~8.66Wh). Your results can swing a bit with cable quality, temperature, and fast-charge settings.
| Typical Load (W) | Estimated Hours* | Common Use |
|---|---|---|
| 0.5W | ≈17.3 h | Earbuds case trickle, LED key light |
| 1W | ≈8.7 h | Fitness band or tiny camera idle |
| 2W | ≈4.3 h | Phone idle/screen off top-ups |
| 3W | ≈2.9 h | Phone light use, GPS standby |
| 5W | ≈1.7 h | Standard USB-A charging |
| 7.5W | ≈1.2 h | Many “fast” 7.5W phone modes |
| 10W | ≈0.9 h | Heavier use or brighter screen |
| 15W | ≈0.6 h | PD/quick-charge burst |
| 18W | ≈0.5 h | High PD burst on capable phones |
*Hours = usable Wh ÷ load in W. We used 8.66Wh (65% of 13.3Wh).
How To Estimate Your Own Runtime
Use these two paths—pick the one that matches what you know.
Path A: You Know The Device Power (W)
- Find your power bank energy in Wh: mAh ÷ 1000 × 3.7V.
- Multiply by an efficiency factor: 0.60–0.70.
- Divide by your device’s power draw in watts.
Example: 3,600mAh → 3.6Ah × 3.7V = 13.3Wh. At 65% usable, 8.66Wh. For a 5W load: 8.66 ÷ 5 ≈ 1.7 hours.
Path B: You Know The Battery Size Of The Gadget
- Convert the gadget’s battery to Wh: its mAh ÷ 1000 × nominal voltage (often 3.7–3.85V for phones).
- Usable power bank Wh ÷ gadget Wh = approximate full charges.
Phone batteries sit around 10–19Wh depending on size. A small 10Wh phone might get close to one full charge; big 5,000mAh phones (≈19Wh) will land under half a charge from a tiny pack like this. The USB spec also matters: higher-voltage quick-charge modes (USB-C PD at 9V/12V/20V) change the conversion path. USB-IF explains the voltage steps on its USB Power Delivery page.
Will It Charge A Phone, And How Many Times?
Yes, but the count depends on the phone’s battery size and how you charge it.
- Small phones (≈10–12Wh): around 0.7–0.9× a full charge.
- Mid phones (≈15Wh): around 0.5–0.7× a full charge.
- Large phones (≈19Wh): around 0.4–0.5× a full charge.
Those ranges assume the pack has near-new cells, decent cables, and you’re not gaming while charging. If the screen stays lit and the CPU/GPU pulls extra current, more of the bank’s energy goes straight to use rather than the battery, which shortens the number of “full” refills you’ll see on the meter.
Fast Charge Vs Trickle Charge
Many phones request a higher voltage over USB-C PD to speed things up. That’s handy when you’re in a rush, but it raises conversion losses inside both the power bank and the phone. A slower 5W-ish charge is easier on efficiency. If you want the most minutes per ounce, slow and steady wins.
How Long Will A 3600mAh Charger Last—Real Usage Cases
Here are grounded, real-world snapshots using the same 65% usable energy assumption. Treat them as ballpark figures rather than lab numbers.
- Maps and screen on (≈5–7W): about 1–1.5 hours of extra time.
- Streaming with screen on (≈6–10W): around 50–90 minutes.
- Phone idle in pocket, trickle top-up (≈1–2W): 4–9 hours of headroom.
- Action cam at 5W: about 1.7 hours of record time.
- Earbuds case (≈1.5Wh battery): five to six full case refills.
- Smartwatch (≈1.1Wh): seven to eight full charges.
Approximate Full Charges By Gadget (65% Usable)
| Gadget | Typical Battery (Wh) | Full Charges* |
|---|---|---|
| Small Phone | 10 | ~0.87× |
| Mid Phone | 12 | ~0.72× |
| Large Phone | 15 | ~0.58× |
| Action Cam | 5 | ~1.73× |
| Earbuds Case | 1.5 | ~5.8× |
| Smartwatch | 1.1 | ~7.9× |
| Handheld Console | 13 | ~0.67× |
*Charges = 8.66Wh ÷ device Wh. Your phone’s exact voltage and cable losses will nudge these up or down.
What Changes The Result
Conversion And Cable Losses
Boosting a cell from 3.7V to 5V or higher wastes some energy as heat. Thin, long, or worn cables add drop on top. Keep the cable short and decent-gauge. If your pack or phone gets hot while charging, losses rise and runtime falls.
Fast-Charge Overheads
PD and other fast modes raise voltage to move energy faster. Great for speed, not so great for total minutes gained per charge cycle. When you have time, stick with a slower profile to squeeze more out of a small bank.
Screen-On Use
Watching video, turning up brightness, or running maps can draw several watts on its own. The bank’s energy then splits: some tops up the battery and some feeds the active load. That’s why a “full charge” count looks worse when you use the phone while it’s plugged in.
Temperature And Age
Cold temps knock down performance. Old cells sag under load and deliver fewer Wh than when new. If your 3,600mAh pack has lived in a hot car, expect less runtime than the math suggests.
Partial Vs 0–100% Refills
Top-ups from 20–70% are gentle and efficient. Pushing a phone battery from the last few percent to 100% slows the charging curve and wastes more energy as heat. If you chase sheer minutes of use, stop early and save those last points for wall power.
Step-By-Step Examples You Can Copy
Example 1: Extra Navigation Time
Your phone draws around 6W with the screen on and GPS running. Usable energy ~8.66Wh. 8.66 ÷ 6 ≈ 1.4 hours.
Example 2: One Light Phone Refill
Your device has a 3,000mAh battery at 3.85V (≈11.6Wh). 8.66Wh ÷ 11.6Wh ≈ 0.75× a full charge. If you charge with the screen off and a short cable, you’ll land near that number.
Example 3: Earbuds Weekend
Your case is roughly 400mAh at 3.7V (≈1.48Wh). 8.66Wh ÷ 1.48Wh ≈ 5.8 charges. That’s a lot of podcasts.
Tips To Stretch A Small Pack
- Charge with the screen off. Brightness is a stealth power hog.
- Use a short, thick cable. High resistance wastes energy.
- Skip heat. Keep the pack and phone out of sun and car dashboards.
- Turn off 5G, GPS, and hotspot while charging if you don’t need them.
- Pick slow charge when time allows. You’ll get a few more minutes overall.
- Stop at ~80–90% if you’re chasing runtime efficiency instead of a 100% meter reading.
Method Notes
All estimates start with a 3.7V nominal cell and convert the label to Wh. We apply a 60–70% real-world window to cover boost conversion, cable loss, and the phone’s charging overhead. Power × time = energy; that’s the basis for the hour figures. If you want the deeper background on energy units, see Battery University’s note on Wh vs W. For USB-C PD voltage steps and higher-power modes used by many chargers and phones, see USB-IF’s USB Power Delivery page.
Bottom Line On A 3,600mAh Pack
A 3,600mAh bank is a “get me home” size. Expect somewhere near one refill for small phones, half a refill for big ones, and plenty of top-ups for wearables. If you need multiple phone charges in a day, step up in capacity; if you just need a safety net, this pocketable size earns its keep.