The service manuel is very helpful, we where able to restore the device to its working operation again.
Text excerpt from page 7 (click to view)
3.
REPLACING THE BATTERIES
1. Loosen the screw on the back of the SF-5300B that holds the battery compartment cover in place, and remove the cover. Loosen the screw that secures one of the two battery holders in place and remove the battery holder. Caution:Be sure to remove only one battery at a time. Otherwise, you will lose all data stored in memory. 3. Replace the old battery with a new one. Be sure that the positive (+) side of the new battery is facing up (so you can see it).
Screw
2.
RESET
4.
Replace the battery holder and secure it by tightening its screw. � Be careful that you do not overtighten the screw. Repeat Steps 2 through 4 for the other battery. � Be sure to replace both batteries. Never mix old batteries with new ones, and be sure to use CR2032 lithium batteries only. After you replace both batteries, replace the battery compartment cover and secure it by tightening its screw. � Be careful that you do not overtighten the screw.
