How do I reset my Casio PRG-40 following battery replacement?

Have the same problem, Casio PRG-80L reads open. No hints about this in the manual. Nor did Votit's suggestion help. Note that although the watch is old there is clearly power left in the capacitor battery. Ended up accidently ito this mode when resetting the time. Assume the open mode is intended for service, but would just like to exit.

You can download a manual/instr from their website. You will have to enter in your country/ model info, etc. Heres the link:

http://www.casio.com/

how do you replace a battery of Casio Pathfinder?

You can find details here: http://world.casio.com/wat/download/en/manual/
Rate me, plz.

You can do it yourself. Unscrew watch caseback and undo the contact on top of battery. Read the writings on battery and buy exactly the same one. Do not mind manufacturers (Casio, Maxell, e.t.c.), just make sure the numbers are the same.
Some watch casebacks can be opened only if the watch band is removed, so, remove it if needed, just don't forget to memorize where every part and screw was fitted. Memorize how the battery is fitted and do not put the new one the other way around as this can damage your watch.
Actually there is nothing difficult - only you have to put everything back exactly the same way as it was. If your watch will be left without battery for more than 3 minutes, you will need to reset your watch after replacing a new battery, but it's easy if you've got users manual.
Good luck.

Do not forget to rate, please.

There is a very small sticker with very small red print just adjacent to the battery compartment. This little sticker states "once batteries are replaced, you need to touch AC with tweezers". I did it with metal tweezers and the watch display came to life. Good luck!

The silver spring goes in a very small hole in the plastic casing on the bottom side of the watch located next to the wristband under the sensor. Hope this helps

If you look very closely you will see that one side of the clip goes nearly under the battery. the plastic there has what looks like a small hole near the metal. It is in fact a slot. use a straight pin inserting it in the slot and gently moving the clip away from the battery. There is bend tension on the clip and it should raise slightly when released. Then use a tweezer grab the battery.

use your tweezer to hook the clip back over th plastic after you insert 4 new batteries.

no, it changed automatically via the atomic satellite that changes all atomic clocks around the world. It so happens you bought a watch that was made in a different, much different time zone. You have been taken.

Your Watch is in Auto or demo mode. Hold down the "Mode" button for 3 - 5 seconds and it will return to time keeping mode.

Cheers,
Murray