That system is at least 30 years old, but Radionics (now Bosch) made solid equipment and chances are good that it's still functional.
See if the Control Panel (NOT the keypad(s) power supply transformer (16.5 VAC, 40VA) is plugged in. It's a beige box (wall wart) plugged into an outlet, usually (but not always) near the Control Panel, the D6112 PCB that lives inside a steel cabinet in some out-of-the-way place. If it's plugged in, make sure there is power at that outlet (plug a lamp or something into it), that the transformer is warm (sometimes hot) to the touch, and if you have a DMM (Digital Multi-Meter), check for output on the terminals, usually 17 to 20 VAC. If your friend doesn't have a DMM (or even an analog multimeter), then s/he needs to get one if s/he's going to do his/her own troubleshooting & fixing. About $15-35 at your local hardware store, you don't need anything elaborate.
If your friend has already checked the transformer, and told you s/he did that---for future reference, tell US s/he already did that, plus anything else s/he already did, so we don't have to describe steps you've already taken.
Once s/he has checked the transformer and replaced the battery (I recommend a 7 or 8 Ah battery), then see if the problem persists. One of the first rules of troubleshooting alarm systems is see to the power supply first, then troubleshoot further.
Please post back and let us know the outcome.
