How to Calculate the Needed mAh for a 3‑Day Hiking Adventure
Updated 2026-08-25 · Power Bank Guide
Planning a multi‑day hike means you have to know how much battery you’ll actually need. By learning how to calculate mAh for hiking, you can pick a power bank that fits in your pack, meets airline rules, and keeps your phone, GPS, and other gadgets alive for the entire trek.
Step 1: Figure Out Your Device’s Energy Consumption
Start with the battery capacity of each device you’ll rely on. Most smartphones list their capacity in mAh, while laptops and tablets use watt‑hours (Wh). Convert everything to the same unit – usually watt‑hours – using the formula:
- Wh = (mAh ÷ 1000) × Voltage
For a typical 3.7 V lithium‑ion cell, a 4000 mAh iPhone battery equals (4000 ÷ 1000) × 3.7 = 14.8 Wh. A 5000 mAh Android phone is about 18.5 Wh, and a 30 Wh tablet is already expressed in Wh.
Step 2: Account for Real‑World Efficiency
Power banks are not 100 % efficient. Internal conversion, cable loss, and temperature can drop efficiency to 60‑70 % for high‑draw devices. To be safe, multiply the device’s Wh by 1.5 (or use 70 % efficiency). Example:
- iPhone 17 battery: 14.8 Wh ÷ 0.7 ≈ 21 Wh needed from the bank.
- GPS handheld (≈5 Wh): 5 Wh ÷ 0.7 ≈ 7 Wh.
- Headlamp or small LED (≈0.5 Wh): 0.5 Wh ÷ 0.7 ≈ 0.7 Wh.
Sum the adjusted values for a total daily requirement. For a 3‑day hike you’d multiply by three.
Step 3: Convert the Total Wh Back to mAh for Your Power Bank
Most power banks are rated at the internal cell voltage of 3.7 V. To find the needed mAh, reverse the earlier formula:
- mAh = (Wh ÷ Voltage) × 1000
Assume your total adjusted consumption is 84 Wh (28 Wh per day × 3). Using 3.7 V:
mAh = (84 ÷ 3.7) × 1000 ≈ 22,700 mAh.
Since power banks are sold in round numbers, a 20 000 mAh unit will cover roughly 70‑80 % of the calculated need, which is usually sufficient if you can recharge a small solar panel or a camp stove charger once during the trip.
Why a 20 000 mAh, Flight‑Safe Bank Is a Good Choice
The INIU 20000mAh Portable Charger (Flight‑Safe) hits the sweet spot for most 3‑day hikes. At 20 000 mAh (≈74 Wh) it stays under the FAA/TSA 100 Wh carry‑on limit, so you can bring it on any domestic flight without checking baggage. Its 22.5 W USB‑C output can fully charge a 14.8 Wh iPhone in about 1.5 hours and a 30 Wh tablet in roughly 2 hours, assuming the 70 % efficiency factor.
Additional perks for hikers include a built‑in flashlight for night‑time emergencies and a USB‑C cable that eliminates the need to pack extra cords.
Practical Packing Tips and Backup Options
Even with a solid power bank, you should plan for redundancy:
- Solar panel: A 5‑W foldable panel can add 10‑15 Wh per sunny hour, extending your bank’s life.
- Power‑saving mode: Turn off background data and use airplane mode when you only need GPS.
- Device rotation: Bring a low‑power backup phone or a dedicated GPS unit to spread the load.
Remember to keep the power bank at a moderate temperature (15‑25 °C) to preserve capacity, especially on hot summer trails.
FAQ
Can I bring a 20000 mAh power bank on a plane?
Yes. A 20 000 mAh bank is about 74 Wh, which is below the 100 Wh limit for carry‑on items set by the FAA and most airlines. Always check the specific airline’s policy before you travel.
How many full charges will a 20000 mAh bank give me?
Real‑world results vary, but with 70 % efficiency you can expect roughly 3‑4 full charges of a 4000 mAh iPhone, 2‑3 charges of a 5000 mAh Android phone, and one charge of a 30 Wh tablet.
Is 22.5 W fast charging enough for a laptop?
22.5 W can top‑up ultrathin laptops (e.g., 45 W‑rated models) slowly, but it won’t replace a dedicated laptop charger for high‑performance machines. For a 15‑inch laptop that needs 65 W, you’ll need a higher‑capacity power bank or a dual‑bank setup.