using a pick or a flathead may be ok but not so neat.
i used a cutter on mine. gently slice the ridges repeatedly on the three straight sides of the battery, thinning the ridges that attach the two pieces of the battery cover. check if you have sliced enough by applying pressure on the sides of the battery, you'll feel the sides giving in. slice a little more, gently ok, don't apply too much pressure while cutting or you'll cut the innards of the battery.
when you think have cut enough, press on the sides of the battery and you'll hear the plastic pop or crack from the pressure. you may then use a small card or a guitar pick to fully separate the cover.
et voila!
