I think you can only ship via RM if you have some kit the lipos connect to BUT not currently connected. I shipped some lipos and sent with a knackered speedo to work within the rules. You do need a special label to say they are lipos.
If you break the rules and the lipos are detected in transit, they are destroyed without compensation.
That was my experience/research. I'm always asked if any batteries at the 2-3 Post offices I use.
I couldn't find a decent price for a courier but YMMV.
HTH
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