12,6V is the voltage over the battery when the charge is done. It will fall afterwards, but I just measured some 3S LiPoes which have rested 4 days since a charging to 12,3V (not a 100% charge!) and they hold 12,1V now. I would have expected something like 12,4 - 12,5 after a 100% charge.
Check the voltage at the battery when the charging is nearly done. This should be 12,6V at the end.

But remember; a cheap DVM might not be accurate... at least not valid for 2 numbers behind ",".