I know and understand why there has been strong restrictions placed on sending lithium ion batteries via air but didn't realise how bad it was even for items like phones (or ebook readers, Amazon Echos etc) with relatively low power non removable batteries (or removable ones where you want to send the battery). Unless I'm missing something, it seems that there's no cheap way to such items overseas anymore.
For sending internationally, NZ Post requires International Express Courier which tends to be very expensive (probably at least $81) https://www.nzpost.co.nz/personal/sending-internationally/prohibited-restricted-items if you follow their rules.
I guess there are some other couriers, maybe they're even slightly cheaper but from my experience these would still be very expensive for randoms sending stuff, I'm guessing at least $60 and frankly I'm not sure if you'll actually finding anything cheaper than NZ Post International Express Courier that accepts such items.
Means if you need to RMA a fairly lower value phone bought overseas, you're in a worse position than I realised. Of course sending via International Air is still not what I'd call cheap & always caried some risk if RMAing due to the lack of tracking if the company you sent it to claims it wasn't received and NZ Post says it was delivered. Still if it's a trustworthy company hopefully shouldn't happen much.
Something to remember when Youshopping etc I suppose.
In retrospect I guess it's not that surprising after the complete ban on lithium-ion batteries as cargo on passenger planes as the normal mail service may them a fair amount. Just not something I really thought about since phones etc are still sent so often (albeit a lot of that is probably in violation, especially those Chinese sellers).