Did Apple replace the battery, or did a third-party or you? Whomever did the battery work likely damaged a sensor or sensor wire. When that happens the system mangement controller (SMC) sets fans to high to avoid heat damage.
You can try another SMC reset--sometime it require two:
If that reset does not restore the fans to normal speed (almost inaudible) then you need to run Apple Hardware Test using instructions in this articele:
It will give a code if it finds anything wrong.