ian field wrote:
The damn thing has developed the habit of bleeping at random intervals, I
tried running it flat and then reconnecting the mains supply but it still
keeps bleeping.

The user manual doesn't have a trouble shooting table and apart from the
random bleeping, the UPS appears to be working correctly.

Any suggestions?

Put a switch in series with the noisemaker. I ran a UPS
with this symptom for years with the alarm disconnected.
AFAICT, the UPS always "did the right thing" (in terms
of power) so the noisemaker was just that -- a maker
of noise. :