Martin,

I had a similar problem with my old GR1000.

This was due to (rechargable) internal battery failure
- which needed to be topped up regularly - every month
in practice.

The Colibri has a Lithium internal battery which 'will
need to be replaced after several years'.
Perhaps it is this battery that is responsible for
your troubles (but failing once a year would seem to
be unlucky).

I understand that the Garmin 12 has a similar problem
and one of my friends, who has had to have the internal
battery replaced, has been advised to switch the unit
on periodically (for some time and preferably using
an outside 12 volt DC source) to keep the internal
battery sweet.

Stan.
UK.