I am working for a company that sells gardening / power tools powered by a Li-ION battery, the device not the offence. (3.6V 1S1P single cell up to 40V 10S2P).
When the customer (private person, John Doe) receives his battery, it is plugged in the device, and thus the package doesn't have to carry the UN3481 label (SP188, Battery in equipment).
John Doe may receive it directly from my company or via (analog) Hardware Store.
Unavoidable as it is, sometimes he wants to return a battery, because it may be defective.
If John returns the battery without the device and because it is believed to be defective, it must be transported as SP376, which includes the packaging according to P908 (ADR126.96.36.199)
Q1) What is the correct way to inform a customer to return a battery without falling into the role of the "Client of the Sender (Auftraggeber des Absenders)"? Is it sufficient to tell him to "return the battery" (zurückgeben) instead of "send the battery back" (zurücksenden)?
Q2) What is the correct way for the customer to return a defective battery with regards to ADR / SP376 / GGVSEB?
Applicable rules: ADR / SP376 / GGVSEB §§17ff
PS: I hope law.se is the correct one, because I haven't found similar questions all over stackexchange.
PPS: I didn't choose the "battery" tag on purpose ;)
PPPS: I know it's common practice to pack the battery just in some carton package to send it, but actually it's against the rules.