Wave Reserve Pocket Power Bank

Details

A flat bank with a short USB-C cable folded into the body, for the days you leave the house with a half-charged phone and no bag. Same arithmetic as the larger Reserve, printed on the back of a smaller object. The mAh number on a power bank is the most successful piece of misdirection in consumer electronics, and the reason it works is that it is not false. The cell really does hold 5,000 mAh, at 3.7 V. Your phone charges at 5 V. Milliamp-hours are only comparable at the same voltage, so 5,000 mAh at 3.7 V can never be more than 5,000 x 3.7 divided by 5, which is 3,700 mAh at 5 V, before a single loss. That is 26 percent gone to arithmetic. Conversion inefficiency then takes about 12 percent more. Nobody prints this, and the honest unit, the watt-hour, is the one unit that appears on no shelf edge in the country. So here it is, laid out to be checked.

• Cell: 5,000 mAh at 3.7 V nominal, lithium polymer pouch. 5,000 mAh x 3.7 V = 18.5 Wh. Both figures on the case, because milliamp-hours alone are not a capacity
• Voltage step: at 5 V that same energy is at most 3,700 mAh. 26 percent of the printed number disappears before anything is switched on, and that is physics, not a defect
• Conversion: measured 88 percent at a 5 V 2 A draw, so 18.5 Wh x 0.88 = 16.2 Wh delivered at the port, which is 3,260 mAh at 5 V. 3,260 divided by 5,000 is 65 percent, and 0.74 x 0.88 = 0.65, so the two routes agree
• In phone charges: a 5,000 mAh 3.87 V phone battery holds 19.35 Wh, and charging it is about 93 percent efficient, so a full charge draws about 20.8 Wh. 16.2 divided by 20.8 is 0.78. This bank gives about three quarters of a phone charge, not the one the number implies
• Output 30 W on the built-in cable or on the separate USB-C port. Input 30 W, empty to full in about 1 hour 10 minutes
• Size 108 x 70 x 15 mm and 152 g. The cell alone is about 77 mL at a pack density near 240 Wh per litre, so a 12 mm body would need a smaller cell. We kept the cell
• Cell replaceable at Rs 590 behind four Torx T6 screws with no adhesive. Built-in cable replaceable at Rs 290. Old cells come back to any Shuunnya LifeStore for recycling
• Protection: over-charge, over-discharge, over-current, short circuit, cell over-temperature cutout at 65 degrees C
• 18.5 Wh, far under the 100 Wh cabin baggage limit, and the Wh figure is printed on the case where airline staff look for it
• The honest trade is thickness. A pocket bank at this energy cannot be 12 mm, and the ones that are hold less than they print
• There is no Shuunnya service-centre network. A warranty claim means posting the bank to us, with no turnaround time promised