Now that you've verified the basics, you can go a step further and test a sample batch yourself. You don't need a lab—just a multimeter and a charger. Check the battery's initial voltage, run a few charge/discharge cycles, and see if it holds a charge. This won't tell you everything, but it catches obvious duds.

Another flourish: use a battery analyzer to check the actual capacity and internal resistance. These devices are affordable and give you a better picture of the cell's health. If you're buying in large quantities, this is worth the investment.

And if you're really serious, send a sample to an independent testing lab for a full safety evaluation. It's not cheap, but for high-volume orders, it's a worthwhile insurance policy.