Kelda 37 · Magnetic power bank · Clay
Power, in plain numbers.
$74.99
A magnetic power bank named for its energy: 10,000 mAh at 3.7 V is 37 Wh. It snaps onto the back of your phone, charges with Qi2 25W, and its plate opens into a stand at 65 degrees.
To charge your phone: snap the pack onto its back, centered, and wireless charging starts. Press the button once to show the pack's level on the readout for 5 seconds. To charge a second device, connect it to the USB-C port: 30 W shared, 15 W + 15 W. To recharge the pack: plug a 30 W USB-C PD adapter (not included) into the USB-C port; with nothing attached it is full from 0% in about 2 h 10 min. Plugged in, it also charges your phone (pass-through), which takes longer. Unplug it when it is full. Stand: swing the plate open and set the phone down in portrait. Hold the button 3 s to switch wireless off or on; switch it off before you pack it.
Shell: polycarbonate with a mineral-matte finish. Stand: anodized aluminum, marigold. Cell: lithium-ion polymer, 1 battery of 2 cells. Cable: braided USB-C to USB-C. Sleeve: wool felt. Box: paper sleeve and molded-pulp tray.
WARNING: Lithium-ion battery. Do not expose to fire, water or high heat, and do not leave it in a hot car or in direct sun. Do not puncture, crush, open or modify. Stop using it and unplug it if it swells, smells, leaks or gets hot to hold. Charge it on a hard, open surface where you can see it, not under pillows or blankets, and unplug it when it is full. Keep away from children and pets. Carry-on only, never in checked bags or the overhead bin. Do not throw it in household trash: recycle it at a battery drop-off or hazardous waste site.
Kelda 37
10,000 mAh at 3.7 V is 37 Wh; rated capacity 6,000 mAh at 5 V 3 A. Every number carries its condition; every charge count is rounded down.
The numbers
10,000 mAh at 3.7 V; rated 6,000 mAh at 5 V 3 A. About 1.5 charges on iPhone 17, 1.3 on 17 Pro, 1.1 on 17 Pro Max (wireless, 0 to 100%, phone idle, 25 °C, our test, rounded down).
Qi2 25W: up to 25 W on iPhone 17, 17 Pro, 17 Pro Max, 16 Plus, 16 Pro Max, 18 Pro and 18 Pro Max; up to 22.5 W on 16 and 16 Pro; up to 20 W on Air; up to 15 W on 17e and 12 to 15. Your phone sets the speed.
One USB-C port, 30 W in and out. Two phones at once: 15 W + 15 W. Plugged in, it charges your phone and itself (pass-through).
In the box
Kelda 37, a USB-C cable, a wool-felt sleeve and The Fine Print card, with every number and its test condition. No adapter: any 30 W USB-C PD adapter works.
How to use
Center the pack on the back of your phone and wireless charging starts. Press the button once to see its level for 5 seconds.
Swing the plate open, up to 65 degrees, and set the phone down in portrait.
A 30 W USB-C PD adapter (not included) fills it from 0% in about 2 h 10 min with nothing attached. Unplug it when it is full.
Hold the button 3 s to switch wireless off before you pack it. Flying: carry-on only.
In daily use
The line: 18.5, 37, 74
 Kelda 18.5 |  Kelda 37 |  Kelda 74 | |
|---|---|---|---|
| Energy (the name) | 18.5 Wh | 37 Wh | 74 Wh |
| Cell | 5,000 mAh at 3.7 V | 10,000 mAh at 3.7 V | 20,000 mAh at 3.7 V |
| Rated at 5 V 3 A | 3,000 mAh | 6,000 mAh | 12,000 mAh |
| iPhone 17 charges, rounded down | 0.7 | 1.5 | 3.0 |
| Wireless | Qi2, up to 15 W | Qi2 25W | Qi2 25W |
| USB-C in and out | 20 W | 30 W | 45 W |
| Thickness | 9.6 mm | 15.2 mm | 26.5 mm |
| Weight | 122 g | 205 g | 365 g |
| Lives in | A jeans pocket | On your phone | Your bag |
The fine print
Model KD37 (Clay: KD37-CL). Lithium-ion polymer, 10,000 mAh at 3.7 V (37 Wh); rated capacity 6,000 mAh at 5 V 3 A. Wireless: Qi2 25W magnetic. USB-C input and output: 5 V 3 A / 9 V 3 A / 15 V 2 A (30 W max); total output 30 W shared, 15 W + 15 W. Stand opens 0 to 65 degrees, portrait. 105 x 70 x 15.2 mm (4.13 x 2.76 x 0.60 in), stand closed; 205 g (7.2 oz). Keeps 80% of its capacity after 800 cycles (our test). Qi ID and FCC ID: on the label under the stand.
Up to 25 W on iPhone 17, 17 Pro, 17 Pro Max, 16 Plus, 16 Pro Max, 18 Pro and 18 Pro Max; up to 22.5 W on iPhone 16 and 16 Pro; up to 20 W on iPhone Air; up to 15 W on iPhone 17e and iPhone 12 to 15, and up to 12 W on iPhone 12 mini and 13 mini. These are peak speeds. On iPhone 17 Pro: 0 to 50% in about 32 min (wireless, phone idle, 25 °C, our test). On iPhone 16e, which has no built-in magnets, use a magnetic case (sold separately).
10,000 mAh at 3.7 V is 37 Wh in the cell. Turning it into phone power warms the converter, the coil and the phone, so about 22 Wh reaches an iPhone 17 battery: about 1.5 charges, 1.3 of a 17 Pro, 1.1 of a 17 Pro Max, 1.7 of an iPhone Air (wireless, phone idle, 25 °C, our test, rounded down).
Yes: the surface is typically 38 to 41 °C (100 to 106 °F) at 25 W in a 25 °C room. Its internal sensor lowers power above 43 °C and pauses at 45 °C until it cools. Temperature monitoring with over-charge, over-current and short-circuit protection; tested to UL 2056.
37 Wh, under the 100 Wh carry-on limit. Carry-on only: keep it with you, never in checked bags or the overhead bin. Hold the button 3 s to switch wireless off, and don't use or charge it on board. Check your airline.
Magnetic cases up to 2.5 mm: about 800 g of pull through 2 mm, about 1,100 g on a bare phone (straight pull, our test). Non-magnetic or thicker cases: add a magnetic ring (sold separately).
Android phones with built-in magnets charge at their own wireless speed; phones without magnets need a magnetic case (sold separately).
Your iPhone holds its battery at 80% when the phone is warm or when optimized charging is on. That is the phone protecting its own battery, not the pack.
WARNING: Lithium-ion battery. Do not expose to fire, water or high heat, and do not leave it in a hot car or in direct sun. Do not puncture, crush, open or modify. Stop using it and unplug it if it swells, smells, leaks or gets hot to hold. Charge it on a hard, open surface where you can see it, not under pillows or blankets, and unplug it when it is full. Keep away from children and pets. Do not throw it in household trash: recycle it at a battery drop-off or hazardous waste site.
iPhone is a trademark of Apple Inc., registered in the U.S. and other countries and regions. Android is a trademark of Google LLC.
About Kelda
A kelda is a spring you can see to the bottom of, so you always know how much is in it. We build power banks the same way. The energy is the name: Kelda 37 holds 37 Wh. Every number has its condition next to it, and every charge count is rounded down. Warm, matte materials, because the pack lives in your hand all day. Marigold inside, because that is where the numbers are.