Originally posted by fabian:
I changed the battery by myself.
3 months later (less actually) - the LOW BATTERY sign is on (again).
I then changed the battery immediately.
3 seconds later - the LOW BATTERY sign is on (yet again!)
As ED mentioned, something that is shorted (or at least electrically leaky) could be the problem. Any competent technician can measure the current being drawn from the backup battery, and determine if it's excessive. While I don't know what the XP50 should normally draw, backup current is often on the order of microamps and some backup circuits draw only nano- or pico-amps, making for years of life even from small cells. Finding a good tech would indeed seem the next step.
By the way, anyone changing a battery (or otherwise working inside modern electronic equipment) would be wise to avoid static discharge. You can easily "zap" many MOS circuits, and sometimes the failure is subtle, as in drawing excessive current while otherwise apparently still working.
--Barry