By Sirius (Intrepid)
This will be added to the FAQ post, but also posting as a new post!
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Battle Markers are quest items that you collect to be able to participate in the Battle Club series of quests once at level 23 on the Pirate Ship. A certain number of Battle Markers is required for entry to each quest in the series. These are as follows:
Battle Club I – 1 Battle Marker
Battle Club II – 10 Battle Markers
Battle Club III – 25 Battle Markers
Battle Club IV – 50 Battle Markers
To see how many Battle Markers you currently have go to:
Shop -> Items -> Quest Items -> Mine and your Battle Markers should be shown in the second drop down list available in that section.
So start collecting them early to ensure that you have plenty available to participate in the Battle Club quests! (Please note that you also have to have completed the previous Battle Club quest in addition to having the appropriate number of Battle Markers available for entry to start the next Battle Club quest. Also, the Battle Markers required are removed from your inventory upon you accepting each Battle Club quest.)

I got a Choatic Blade III
But I haven’t get a quest to level it up to IV
and now I’m lv 16
give me a hand please
Have you been back to the Swamp to see the Smithy there, as the Quest can only come from the Swamp? If you have, and it’s definitely not available there currently, perhaps you need to be level 17 before receiving the Quest.