help please w/ PD Worldtimer Alarm question

My Worldtimer stopped so replaced battery. When closed case the watch alarm activated and the watch is now just running about half speed. Bad battery? the battery replaced was a 397/396 and battery shop sold me a 396; perhaps different (lower) power output? Hopefully not being really dumb here but feeling like it! Thanks for any insights!!

The battery fits. Maybe a contact problem ?!

Silberoxyd Uhrenbatterie Type 397 / 396:

Varta V397 - V396
Bulova 607
Citizen 280-28
Duracell D397 - D396
Energizer 397
GP Sylva Cell 397
IEC SR59
Panasonic SR726SW
Maxell SR726SW
Ray-o-vac 397
Renata 397
Seiko SB-AL
Sony SR726 SW
Timex N
Toshiba SR 726 SW
Ucar 397
Technische Daten:

System: Silberoxyd Batterie
Spannung: 1,55 Volt
Kapazität: 30mAh
Maße: 7,9x2,6mm

Thanks! - checked the contacts, reinstalled battery, etc. Alarm button works but still running slow. second hands moves two clicks, then hesitates and goes again.
The run pattern may be described in the instruction booklet but I've misplaced mine

Hm, "second hands moves two clicks"
This usually indicates LOW BATTERY ?????

I would really try another NEW battery.

Sorry for this proposal, but this try is cheap and simple ?!

Your watch will tell you that the battery needs replacing when the second hand suddenly starts to jump four seconds at a time.
Your 2 second jump and stutter indicates too much friction in the train wheels. The oil may be dry or dust may have entered during the battery change.
Your watch needs to be serviced.
P.S.
397 battery is high drain so will last longer than 396 if you frequently use the alarm.
Leo

POR0286 as a new member of the forum you will not know that Leo knows the inside of loads of IWcs and has access to IWC data as he is the service manager in London.