A Day-Bag Power Bank for Indoor Top-Ups: Small 5K or Larger 10K?

How much backup do you actually need?

The Anker has a 5,000mAh battery; the Belkin has 10,000mAh. The smaller option makes sense if you usually need a top-up before getting home. The larger one is the more useful starting point when you routinely need more backup between opportunities to recharge the bank.

Those numbers are not a promise of one versus two full phone charges. Battery-cell capacity is not the same as energy delivered to your phone: voltage conversion and charging losses matter. Your phone's battery size and use while connected also affect the result. Neither capacity guarantees that a particular phone will last all day.

If the bank you already own comfortably covers your routine, there is little reason to replace it just for a bigger number.

Smaller body, or more room in your bag?

The Anker weighs 3.5 ounces (100g) and measures about 3 inches long by 1.5 inches wide. The Belkin is about 3.9 by 2.5 inches. Both are roughly an inch thick, so the Belkin's larger footprint is the more noticeable packing difference.

For a small pocket or compact pouch, the Anker is the easier shape to accommodate. For a day bag with space to spare, the Belkin trades more room for its larger nominal capacity.

The connection changes how you hold your phone

The Anker's folding USB-C plug can remove the need for a loose cable, but it attaches the bank directly to the phone. Anker says to support both devices while charging and excludes cases thicker than 0.19 inch (4.9mm). A case opening still needs to let the connector seat properly. You can instead use the included USB-C-to-C cable with the bank's USB-C port.

The Belkin's attached USB-C cable gives you a short flexible connection rather than a rigid plug under the phone. It is only about 2.2 inches long, not a cable for leaving the bank deep in a bag while using the phone. Its separate USB-C port lets you use your own longer cable.

These built-in connectors fit USB-C phones, not Lightning iPhones. A Lightning phone needs a separate suitable USB-C-to-Lightning cable through the bank's USB-C port.

Sharing and refilling have limits

The Belkin supplies up to 20W through either its cable or USB-C port when used alone. Connect two devices and they share up to 15W total, not 20W each. That makes its second connection useful for convenience, not for maintaining the single-device maximum.

The Anker accepts up to 18W input; the Belkin accepts up to 20W. Neither includes a wall charger. A compatible USB-C power source is needed to refill them, and these input ratings do not establish how long a full refill takes. Likewise, the Anker's 22.5W name does not promise that speed for every phone.

Keep charging dry and within the manufacturers' 32–95°F (0–35°C) operating range. Do not use a damaged bank. These are indoor top-up choices, not weatherproof power supplies.

Choose your option

Smaller backup: Anker Nano 5K

A compact 100g body, folding USB-C plug and included 2-foot USB-C-to-C cable suit modest phone top-ups.

Keep in mind: Less nominal reserve; the direct plug requires case clearance and support for both the phone and bank.

View on Amazon: Smaller backup: Anker Nano 5K (opens in a new tab)

Larger reserve: Belkin BoostCharge 10K

A larger 10,000mAh nominal capacity and attached USB-C cable suit longer gaps between refills at indoor stops.

Keep in mind: A larger footprint, very short attached cable and indoor-only recommendation; two devices share 15W.

View on Amazon: Larger reserve: Belkin BoostCharge 10K (opens in a new tab)

Based on the manufacturers’ specifications and instructions and the selected Amazon listings, checked October 18, 2026. We have not hands-on tested these power banks.