For today's ever more tech-savvy and power-hungry populace, power banks are increasingly popular options to help people stay connected throughout the day. However, the most important parts of these products' quality is impossible to discern by outward appearance alone. Verifying the capacity of power banks can take hours of time that many are not willing to invest. The best solution seems to be finding reliable companies and sticking with them.

"In the past, when we first started out, every single battery cell we'd buy from the supplier, we'd do the test, but that's very time consuming," said Wei Zheng, sales manager of power bank supplier ETycho. "Now we just make sure we just do business with reliable battery cell suppliers."

Zheng added that ETycho continues to randomly check battery cells, as well. Some power bank companies might not be as scrupulous as others, though, so buyers of the power banks also remain vigilant and look for reliable suppliers.

While Zheng said the most accurate way to measure capacity of a battery is with expensive specialized equipment, some people are using phone apps to gauge how much power the devices hold. This was the case with a couple buyers from a Latin American promotional company who asked not to be identified to avoid angering their suppliers. The buyers said quality issues come up at any fair in any product category.

Calvin Ng of the Malaysia-based distributor Global Synergy said he also uses his phone to check power banks by running through a few cycles. Ng said he avoids less established companies, preferring brands he knows will help fix any problems he has with the products.

There are a number of factors that can result in the sale of under-capacity batteries. Zheng said suppliers are under pressure to get orders out, and the very competitive market probably does not help matters as manufacturers look for ways to keep prices down. This can result in cutting corners and even putting out faulty products, Zheng said.

“Like any other products, there are going to be some faulty ones that are below expected capacity,” he said. “What do they do with it? They can trash it or they can try to sell it on the market to salvage whatever value they can get out of those lower quality units.”

Zheng also said cell manufacturers like to have some of the expensive machines available for buyers to see, giving the impression of good quality control. These machines might never or rarely be used, though, because the process of checking capacity is very time consuming.

The preference for sourcing power banks in China seems to be finding reliable suppliers. Power bank suppliers have cell manufacturers they trust, and power bank buyers have suppliers they trust. Still, it would be a foolhardy business practice to completely put one’s business in the hands of a third party, so buyers prefer to follow the old maxim “trust, but verify” by conducting random checks to ensure their trusted partners are maintaining quality.