Most companies wont take any battery over 100wh that is not connected to its device
Royal mail will dispose of any battery they find in their system that does not meet their criteria and will offer no compensation , if you do send it via RM without telling them you also run the risk of prosuction if the battey were to cause a fire
There are companies that will take batteries over 100wh that are not connected to their device (shops post out e bike batteries to customers who want a spare) but i have struggled to find a company who wwill do this for a 2nd hand battery, most will only accept brand new batteries being sent via a business account (companies selling batteries are more trusted to package the battery properly and safely compared to the public)
Collect plus will not take batteries and will not offer any compensation and will hold you liable for any damages, costs or expenses resulting from your parcel (its in their terms and conditions)
Parcel Monkey wont even accept kids toys or electronics with batteries in them they have to be removed, they wont take sat nav’s camera’s etc.. as they have built in batteries
Most companies have had a clamp down on lithuim batteries in the last year or so due to quite a few plane fires, once a battery catches fire they are very hard to put out
In short its bloody hard to find someone to take a 2nd hand 100wh+ battery legally and safely!