Stop buying by mAh: How to choose the right portable power bank for laptops, tablets, and smartphones

Buying a portable power bank by “mAh” alone is why many people end up disappointed. What really matters is watt-hours (Wh), output wattage (how fast it can charge), and real-world efficiency.

This practical buyer’s guide gives you:

• A 60-second Wh + wattage calculator to size your bank for phones, tablets, and laptops
• Clear rules of thumb with real examples (10k / 20k / 30k+)
• A device-matching flowchart and a cable checklist
• Airline-safe picks and safety tips

What you’ll walk away with: the exact capacity and output you need, how many charges to expect, which USB‑C Power Delivery levels to choose for fast charging, and which cables make or break performance. If you want a smartphone power bank for daily top-ups, a power bank for tablets for trips, or a laptop power bank for work, this guide keeps it simple.

The 60‑second watt‑hour + wattage calculator (get the right size fast)

Stop guessing “how many mAh do I need?” Use Wh. Watt-hours standardize battery capacity across devices and map to airline rules.

Quick math (mAh to Wh conversion):

• Convert mAh to Wh: Wh ≈ mAh × 3.6 ÷ 1000
• Convert Wh to mAh: mAh ≈ Wh × 1000 ÷ 3.6

Plan for losses (power bank efficiency):

• Real use is ~60–75% efficient (cable quality, heat, device load)
• Safe shortcut: estimate with 70% efficiency

Size your portable power bank:

• Find your device battery (Wh). If you only see mAh, convert it.
• Pick your target: number of charges or extra hours.
• Bank Wh needed ≈ (device Wh × target) ÷ 0.7
• Then check output wattage needs (below).

Quick, realistic “calculate number of charges”:

• Charges ≈ (bank Wh × 0.7) ÷ device Wh
• This reflects real capacity vs rated capacity.

Common device battery sizes (watt-hours Wh):

• iPhone 15/16: ~12–13 Wh
• iPad Air/Pro 11": ~28–30 Wh
• MacBook Air 13": ~52 Wh
• 14–16" performance laptops: 70–100 Wh

How to size a power bank for a laptop (important):

• Match output wattage to your workflow.
  • Browsing/notes: 20–35W draw
  • Light productivity: 35–60W
  • Heavy loads/gaming: 60–100W+
• If the bank’s USB‑C PD output is lower than your laptop’s demand, it may hold the battery steady but not charge it fast—or not at all. This is the key to charging laptops with a power bank reliably.

Reddit pro tip:

• For gaming laptops, switch to “Hybrid/Integrated GPU” or “Battery Saver” on a laptop power bank. Users report better stability and faster PD charging with these modes.

Quick sizing rules and real‑world examples (10k / 20k / 30k+)

Rules of thumb (battery capacity tiers):

• 10,000 mAh (~36 Wh): best as a smartphone power bank for a day or two
• 20,000 mAh (~72 Wh): phones + tablets, and can top up small laptops
• 27,000–30,000 mAh (~99–108 Wh): light laptops (MacBook Air class) and longer trips
  • Note: 27k (≈100Wh) is airline‑safe; many 30k banks exceed 100Wh and may require airline approval
• 40,000–50,000 mAh (144–180 Wh): camping and big laptops; not airline carry‑on under standard rules

Real‑world outcomes (assume ~70% efficiency):

• 10k: about 2 iPhone charges; roughly 0.8 iPad charge; ~0.5 MacBook Air charge
• 20k: about 3–4 iPhone charges; ~1.6–1.8 iPad charges; ~0.9–1.0 MacBook Air charge
• 30k: about 5–6 iPhone charges; ~2.3–2.6 iPad charges; ~1.3–1.4 MacBook Air charges

Is 20000mAh enough for a laptop?

• For light laptops (Ultrabooks/Chromebooks/MacBook Air): yes, for one near‑full charge, if the bank has 65W+ USB‑C PD output.
• For 14–16" or performance laptops: consider a 30000mAh power bank for laptop with 100–140W PD, or expect shorter runtimes.
• For camping or long days: a 50000mAh power bank or compact portable power station is smarter (not flight‑friendly).

Output standards that actually matter (PD, PPS, QC, and AC)

USB‑C Power Delivery tiers you can trust (fast charging):

• Phones: 20–30W PD
• Tablets: 30–45W PD
• Most laptops: 65–100W PD (look for a 65W USB‑C PD power bank or a 100W USB‑C PD power bank)
• High‑draw laptops (e.g., 16" MacBook Pro): PD 3.1 EPR 140W

PPS (Programmable Power Supply) for Samsung and some Pixel phones:

• Smoother voltage/current adjustment, less heat, better efficiency, and sustained fast charging

Quick Charge 3.0 compatibility:

• Useful for older phones/accessories, but for modern ecosystems, PD is the standard
• PD power bank vs QC power bank: choose PD if you want laptop and tablet support

AC outlet power bank vs USB‑C PD:

• AC outlet power banks are bulkier and less efficient (DC→AC→DC losses)
• If your laptop supports USB‑C PD, direct PD is better
• Use AC outlet banks for legacy barrel‑jack laptops only

Reality check on PD 3.1 EPR 140W:

• Treat 140W as peak. Under heat, many devices step down to ~100–120W. That’s normal and still fine for most laptops.

Reddit pro tip:

• Many dual‑port banks share one PD controller. When you plug in two devices, voltages and currents may downshift. Don’t assume 20V and 12V at the same time unless the spec says so.

Ports, cables, and simultaneous charging (what spec sheets don’t tell you)

• Dual USB‑C ports: The combined output is often shared. With multiple device charging, expect one or both to slow down.
• Charge laptop and phone simultaneously: Read the shared output table; many banks can’t keep 20V for a laptop if the second port negotiates 9–12V at the same time.
• Cable essentials (USB‑C to USB‑C cable quality matters):
  • For 100–140W, use an e‑marked 5A USB‑C to USB‑C cable
  • Keep cables short and high quality to reduce voltage drop
• Pass‑through charging: Most high‑power banks skip it due to heat and safety. It’s safer and faster to use a GaN wall charger to refill power bank.
• Nice‑to‑have features: trickle charge mode / low current mode for earbuds and watches, a battery percentage indicator or digital display power bank, and built‑in cables/adapters.
• Input speed matters: USB‑C input 45W or higher cuts downtime by hours (recharging speed input is easy to overlook).

Reddit pro tip:

• Cable direction/orientation can matter on some high‑power setups. If a 140W PD link is flaky, re‑seat or flip the cable ends, and try another certified 5A cable.

Device-by-device compatibility and tips

Charging laptops with a power bank:

• Check that your laptop supports USB‑C PD input (not all do)
• Match or exceed the required output wattage (common: 65W, 100W; some need PD 3.1 EPR 140W)
• Gaming laptops may still prefer their AC bricks; a PD bank can slow the drain or top up during light use

Windows laptop USB‑C charging, Chromebook power bank, Surface Pro USB‑C charging:

• Update BIOS/firmware
• Use a 100W‑rated USB‑C PD port and an e‑marked 5A cable
• If it won’t charge: try another port, disable “performance” power modes, or reboot with the bank connected

MacBook Air/Pro power bank tips:

• MacBook Air runs well on 30–67W PD
• MacBook Pro 14–16" benefits from 100–140W PD; sustained 140W is not always needed for normal work

Tablets and phones:

• iPad charging with power bank: 30–45W PD is ideal
• Android tablet charging: target 30–45W PD; PPS support helps with heat
• iPhone USB‑C power bank: 20–30W PD delivers fast charging (use USB‑C to USB‑C)
• Samsung Galaxy power bank: PPS support improves fast charging stability

Why won’t my laptop charge from a power bank?

• No USB‑C PD input support on the laptop
• Cable not e‑marked 5A when trying 100–140W
• Bank can’t negotiate the needed PD profile (try single‑port use)
• Power mode too high; the laptop draws more than the bank can supply
• In rare cases, use an AC outlet power bank for legacy barrel‑jack models

Reddit pro tip:

• If a second device causes your laptop to drop from 20V to 12V, your bank likely shares a PD controller. Charge the laptop alone, or use a bank with independent outputs.

Travel, safety, and airline rules

Airline rules simplified:

• Standard IATA limit: ≤100 Wh per battery (about 26,800–27,000 mAh) in carry‑on only
• Some airlines allow up to 160 Wh with approval (check policy)
• “Airline limit 26800mAh” is a common label shorthand; always confirm the Wh marking

What security looks for:

• Watt-hours Wh printed on the label (airline‑approved labeling helps)
• UN38.3 certified battery, plus safety certifications UL/ETL, CE, FCC

Safety features that matter:

• Overcharge, over‑current, over‑temp, and short‑circuit protection
• Brand transparency, clear support pages, recall history, warranty and support, and strong customer reviews and reliability

Travel checklist:

• Carry‑on only, never checked
• Use terminal caps and a case to protect ports
• Be ready to show Wh rating for big‑capacity banks when asked

Reddit pro tip:

• 100Wh ≈ 27,000 mAh (at 3.6V). If your bank shows only mAh, convert before you fly.

Size, weight, and use‑case picks

Match capacity to how you move (size and portability):

• Everyday carry: slim power bank for phone (10k). A credit card power bank is great for quick top‑ups.
• Travel/work days: 20k with 65–100W PD for phones + tablets + light laptops; good balance of capacity vs weight.
• Weekend/camping: 30k–50k with 100W+ PD; for longer trips, a compact portable power station is best.

Rugged and solar‑ready:

• Rugged waterproof power bank models exist, but solar on a power bank alone is slow. For camping laptop charging, pair a real solar panel with the bank.

Remote work travel kit:

• 65–100W PD laptop power bank, e‑marked 5A USB‑C cable, and a 100–150W GaN wall charger to refill the bank fast

Brands, reliability, and what to buy at each budget

How to judge value (price per watt‑hour):

• Price per Wh, sustained output without overheating, and heat management
• Clear safety certifications and a solid warranty
• Verified customer reviews and brand support; check recall pages

Notable options (one‑time mentions):

Mid‑range 20k, high output: UGREEN Nexode Power Bank 20,000 mAh 130W with TFT display (≈72Wh, airline‑approved).

Baseus Blade HD 20,000 mAh 100W, a slim design with digital display.

Premium 100W+ or PD 3.1: SHARGEEK 140 Power Bank 20,000 mAh, up to 100W USB‑C + 40W USB‑A, transparent case.

Anker Prime 27,650 mAh 3‑Port 250W (≈99.5Wh, airline‑safe), PD 3.1 multi‑device.

AC outlet power bank (for legacy barrel‑jack laptops): Omni 20+ 20,000 mAh/71Wh with 100W AC, 60W USB‑C PD, adjustable DC, and wireless charging.

Also look at established names like Zendure, Nitecore, Mophie, and UGREEN for varied form factors. If you need to power multiple large devices for hours or run AC gear, an EcoFlow or Jackery portable power station (or Goal Zero) beats a power bank on flexibility—at the cost of size and weight.

Note: Major brands sometimes issue recalls for safety. Check model numbers and follow replacement instructions if applicable.

Recharging the bank quickly (don’t forget input speed)

Input wattage = downtime. A bank that only takes 18–20W input can need all night to refill.

Fast refill tips:

• Pick USB‑C input 45W or higher (65–140W is even better)
• Use a quality GaN wall charger to refill power bank and an e‑marked 5A cable

Handy picks (one‑time mentions):

A 150W GaN wall charger (4‑port) refills high‑capacity banks quickly and can power multiple devices at once.

A 240W e‑marked USB‑C to USB‑C cable (5A) is required for reliable 100–140W PD performance.

Rough recharge time estimates (including overhead):

• 20,000 mAh (72Wh) at 45W input: about 2–2.5 hours
• 27,000 mAh (99Wh) at 65W input: about 2–3 hours
• If your bank supports higher PD input (e.g., 100W+), times can drop below 2 hours

A digital display power bank or accurate battery percentage indicator makes planning much easier.

Flowchart and checklist: match your device, bank, and cable

Flowchart (simple):

• What are you charging?
  • Phone → target 25–30W USB‑C Power Delivery (fast charging) → pick 10k–20k for daily/travel
  • Tablet → target 30–45W USB‑C PD → pick 20k (or 27k for multi‑day)
  • Laptop → check your charger wattage
    • ≤65W → pick a 65W USB‑C PD power bank; 20k–27k
    • 65–100W → pick a 100W USB‑C PD power bank; 27k–30k
    • 100–140W → pick PD 3.1 EPR 140W; 27k–30k (airline‑safe) or larger for off‑grid

Cable checklist:

• 100–140W: e‑marked 5A USB‑C to USB‑C
• Samsung/Pixel fast charging: PPS support for Samsung, quality USB‑C cables
• Keep cables short to reduce loss
• Bring only the adapters you truly need

Good / better / best PD targets:

• Phones: 25–30W
• Tablets: 30–45W
• Most laptops: 65–100W
• High‑draw laptops: 140W PD 3.1 EPR

Reddit pro tip:

• Many high‑power banks don’t support pass‑through charging. Refill the bank with a GaN charger instead of trying to use it as a mini‑UPS.

Frequently asked questions

How many charges for iPhone?

• Use the quick math: charges ≈ (bank Wh × 0.7) ÷ 13 Wh
• 10k bank: about 2 charges; 20k: about 3–4; 30k: about 5–6

How many charges for iPad?

• For a ~29 Wh iPad: 10k → ~0.8x, 20k → ~1.7x, 30k → ~2.4x

Can a power bank charge a laptop?

• Yes, if it supports USB‑C PD at the right wattage (65–140W). Use an e‑marked 5A cable for 100W+.

Why won’t my laptop charge from a power bank?

• No USB‑C PD input on the laptop, wrong cable, shared‑port limits on the bank, or laptop power mode is too high. Try a single PD port, correct cable, and lower power mode. For legacy barrel‑jack laptops, use an AC outlet power bank.

Is pass‑through charging safe or useful?

• Many makers avoid it on high‑power models due to heat. It’s safer to refill your bank first with a solid GaN charger, then charge devices from the bank.

Is it safe to use a power bank while charging my phone?

• Yes. Use proper cables, avoid covering the bank (let heat escape), and watch for excess warmth.

Multiple device charging tips:

• Expect shared output limits. Your laptop may drop from 20V to 12V if you plug in a second device.

PD power bank vs QC power bank?

• PD is the modern standard for laptops, tablets, and new phones. QC 3.0 is fine for older phones but not for laptops.

Traveling with batteries: TSA and IATA reminders

• Carry‑on only. Standard IATA 100Wh limit (about 27,000 mAh). Some airlines allow up to 160Wh with approval. Keep the Wh label visible.

Glossary and spec decode (quick reference)

• mAh: milliamp‑hours; not great for comparing different voltages
• Watt‑hours (Wh): true “size” across devices; use this for flights and real runtime
• USB‑C Power Delivery (PD): fast charging standard for phones, tablets, and laptops
• PPS: fine‑tuned PD for Samsung/Pixel; better heat and efficiency
• PD 3.1 EPR: extended power up to 140W via USB‑C
• Output wattage: the maximum speed a bank can deliver (e.g., 45W, 65W, 100W, 140W)
• Efficiency: you never get 100% of the rated Wh; plan for ~60–75%
• Real capacity vs rated capacity: real usable energy is lower due to conversion losses

Reddit pro tip:

• Treat marketing “max watts” as peak. Expect some step‑down under heat. For a 16" MacBook Pro, 100W sustained is usually fine after the initial burst.

Safety reminder: Look for UN38.3, UL/ETL, CE, FCC marks; register your product and check brand recall pages before travel.