I checked on Easyjet website and it says this:They will want to see it has the CE mark on an official manufacturers label one would expect.
"Spare Lithium batteries Lithium ion batteries for portable (including medical) electronic devices, a Wh rating exceeding 100Wh but not exceeding 160 Wh. For portable medical electronic devices only, lithium metal batteries with a lithium content exceeding 2 g but not exceeding 8 g. Maximum of two spare batteries in carry-on baggage only. These batteries must be individually protected to prevent short circuits."
Looks like for europe I can carry up to 160wh? So a 125wh battery would be ok?