Earlier, I had made a post regarding the prohibited shipment of batteries containing lithium, such as coin-cell batteries:
Batteries *not* included? 🙁
After a review of USPS guidelines for allowable shipments, I can safely say that is no longer necessarily the case:
349 Miscellaneous Hazardous Materials (Hazard Class 9)
It seems that bulk shipments of more than 4 batteries, or more batteries than necessary to operate a device, must be marked with fire hazard warning stickers. Since each item is only shipped with enough batteries to operate them, this is no longer a problem. Therefore, USPS will be used again for all shipping needs, as previously considered.
I apologize for any inconvenience this may have caused in the meantime.