Ampax Modular Power Bank Brings Replaceable 21700 Cells to the Portable Charger Market

The Ampax power bank arrives as a compact, modular solution that lets you swap out its two 21700 lithium‑ion cells when they run out of juice. Each cell is rated at 5 000 mAh, so together they deliver a nominal 10 000 mAh capacity, or about 37 Wh at 3.7 V. In practice that translates to roughly three full charges for a typical smartphone, or a single charge for a mid‑range laptop that accepts USB‑C power delivery.

What’s new?

• Replaceable 21700 cells – Unlike sealed power banks, the Ampax lets you pop out the batteries and insert fresh ones. The cells are standard 21700 format, widely used in high‑performance flashlights and some electric‑bike kits, meaning many enthusiasts already own spares.
• Dual output ports – One USB‑A and one USB‑C port can operate simultaneously, delivering up to 22.5 W total (5 V / 3 A on USB‑A, 9 V / 2.5 A or 12 V / 1.875 A on USB‑C). This is enough for fast‑charging a phone while topping up a tablet or wireless earbuds.
• Crowdfunded price – The Kickstarter campaign lists the base unit at $36, with a $50 tier that adds a four‑cell charger compatible with the same 21700 format.

How it stacks up against the competition

Feature	Ampax	Typical sealed power bank	Similar modular kits (AliExpress, Amazon)
Cell type	21700 (replaceable)	Integrated 18650/21700	21700 (replaceable)
Capacity	10 000 mAh (37 Wh)	5 000‑20 000 mAh (varying)	8 000‑12 000 mAh
Output power	22.5 W total (USB‑A + USB‑C)	15‑30 W (often USB‑C only)	18‑25 W
Price (base)	$36	$20‑$60	$30‑$45
Spare‑cell strategy	Carry extra 21700s	Carry extra power banks	Carry extra 21700s

The Ampax’s main advantage is the ability to keep a small stock of spare 21700 cells. A single spare adds roughly 5 000 mAh, which is lighter and more space‑efficient than lugging an additional 200 g power bank. However, the overall energy density is still lower than the largest sealed power banks that pack 20 000 mAh in a single enclosure.

Who will benefit?

• Field technicians and outdoor enthusiasts who already use 21700 batteries in flashlights or portable tools. They can repurpose existing cells and avoid buying a dedicated spare charger.
• Minimalist travelers who prefer a single, lightweight unit that can be refueled with a spare cell rather than multiple bulkier chargers.
• DIY hobbyists who like to tinker with battery management. The included charger (available at the $50 pledge level) supports four cells, making it easy to keep a rotating stock of fully charged packs.

Conversely, casual smartphone users may find the modular concept unnecessary. For them, a conventional sealed power bank with a single high‑capacity cell is simpler and often cheaper in the long run.

Potential drawbacks

• Supply chain risk – The Kickstarter model means you won’t receive the unit until at least August, and there’s always a chance the campaign falls short of its target.
• Battery management – Swapping cells requires careful handling to avoid short circuits or reverse polarity. Users must ensure the cells are matched in voltage and health.
• Limited fast‑charge support – While 22.5 W is adequate for phones, it falls short of the 45‑W+ USB‑PD rates that some newer laptops demand.

Bottom line

The Ampax modular power bank offers a practical niche solution for users who already own 21700 cells or who value the ability to carry spare batteries in a compact form factor. It isn’t the first product of its kind, but its Kickstarter price point and the inclusion of a four‑cell charger make it an attractive entry for enthusiasts willing to accept the typical crowdfunding risks.

For more details on the campaign and to back the project, visit the Kickstarter page.