You can't change the battery without opening the back and that WILL compromise the seal. The question is whether you can re-seal the watch and be certain that you still have 200 metre water resistance. The back is a snap-on back which can be removed by levering off with a penknife blade. You can buy a replacement battery easily enough, and probably a replacement rubber seal (from Casio) as well. But unless you have a watch pressure testing tank costing a few hundred pounds you have no way of KNOWING that the watch is still water resistant for, for example, scuba diving. Very few jewellers shops have this equipment, but if you can find one it will probably be cheaper than sending your watch back to Casio. If you don't need a guarantee of water resistance, go ahead and change the battery yourself - it's quite easy.
Andy, January 2008
