Big Red

While lithium batteries are fairly good, I can tell you an advertisement for an 80,000 mAh USB battery bank is a scam. 80 amp hours even at just 5 volts, is 2/5th of a kilowatt hour — which is a lot of electricity to store in a little battery.

The 50 lb lead acid batteries in my truck — each only have about 50 amp hours of usable capacity (to be fair, at 12 volts). Trust me, you’re not going to take a 50 lb battery to the beach to charge your cellphone.

What are they doing to make this claim?
1) First off they’re measuring amp hours at the nominal voltage of the lithium ion batteries at 3.6 volts, ignoring losses in the boost converter, and that 1 amp at 3.6 volts is only 0.72 amp at 5 volts. But discount by the 80% with loses in the boost converter, so you are at .57 amp at 5 volts.

2) A really good 18650 cell — like a pricey one used in an electric car or high end laptop might have 3.5 amp-hour capacity. So the best case scenario if there is three really good 18650 cells in this unit, it could put out 10.5 amp hours or 10,500 mAh if your interested in inflating numbers.

3) But with loses in the boost converter, and the fact that when you increase voltage you decrease amperage, your talking about 5.98 amp hour or 5,980 mA hour if you want to sound impressive. But I doubt the Chinese cheapout 18650 cells in this put anywhere near that capacity.

So yes, these solar chargers are a scam. The solar cells themselves put out maybe 20 – 30 mAh of capacity, so don’t expect much charging unless you have days in the direct sun.