Buying a power bank should be simple, but the specs printed on the box can be misleading. Here is a practical checklist covering the things that actually matter before you hand over your money. A longer, Indonesian-language version of this guide with detailed calculation walkthroughs lives on my blog.

1. Read the rated capacity, not just the big mAh number

The headline mAh figure is the raw battery cell capacity measured at 3.7V. The energy figure that actually matters is watt-hours (Wh): mAh x 3.7 / 1000. So a "20,000 mAh" pack holds 74 Wh of energy. After voltage conversion up to 5V USB output at roughly 85-90% efficiency, the effective capacity you can actually use is around 17,000-18,000 mAh. Check the rated capacity printed on the unit itself to see a realistic number. One honest caveat: these figures come from calculation using the manufacturers' formulas, not from physical hardware measurement — no spec sheet can promise you the exact real-world output of your particular unit.

2. Match the fast-charging protocol to your phone

Find out which fast-charging protocols your phone supports — USB Power Delivery (PD), Quick Charge (QC), VOOC/SuperVOOC, or PPS — and buy a power bank that speaks the same language. A 65W PD power bank paired with a phone that only supports VOOC will still charge at slow speed. Mismatched protocols are the most common reason "fast charge" refuses to kick in.

3. Insist on two-way USB-C

A USB-C port that both recharges the power bank (input) and charges your devices (output) means a single cable does everything. Older packs with micro-USB input are an inconvenience you should not accept in a new purchase.

4. Know the airplane rules

Spare lithium batteries are restricted in carry-on baggage: under 100 Wh needs no approval, 100-160 Wh requires airline approval, and anything over 160 Wh is banned from passenger flights. Most 10,000-20,000 mAh packs sit at 37-74 Wh, so they fly fine — just verify before buying an oversized one.

5. Look for real safety protections

A trustworthy power bank lists protections against overcharge, over-discharge, short circuits, and overheating, ideally backed by recognized certifications. If a brand lists none of these, treat that as a red flag.

6. Learn to spot fakes

Counterfeits are everywhere. A unit that feels suspiciously light for its claimed capacity, packaging without rated-capacity printing, and sellers outside official channels are all warning signs. Buy from official stores or authorized retailers, not the cheapest random listing.

7. Size the capacity to your needs

10,000 mAh is enough for a daily top-up of one phone; 20,000 mAh fits weekend travel and multiple devices. Bigger packs weigh noticeably more, so do not overbuy.

This is a syndicated English version of my Indonesian article "Cara Memilih Powerbank yang Bagus: 7 Hal yang Wajib Dicek Sebelum Beli" — that original is the canonical version.