Can’t turn on speaker even when it’s charged

Must be frustrating. If it were me, I might let the battery fully drain before recharging it a bit again and retrying.

Could the 'On' or other switches be the culprit? An inspection and cleaning of them if possible may help. I realize

waterproofing covers and such can make this an involved process.

91% or purer denatured alcohol or spray electronics cleaner in the contacts can sometimes remedy problems beautifully.

If none of these help, I would also consider disassembling and unplugging the battery from the speaker. Touching all the switches while unpowered and then reconnecting the battery to the speaker (before fully reassembling) to see if that helped (not likely, but possible). The battery may also be just plain dead and need replacement despite its relative newness. That happened to me with one of my own bluetooth speakers of a different make and model. I replaced the battery and it now recharges and works like a gem.

Good luck!