could be cold batteries, battery performance deteriorates at low temperatures

So cloudy weather is the common denominator. I have trawled the web but not found any justification or reason for this behaviour.

The other odd thing is that my batteries did not seem to take long to get to full charge again today. That might imply that they were not fully run down. Who knows

Odd. I was out running for three hours yesterday with iPod and the fully charged batteries, normally good for several hours, gave up the ghost after 65 minutes. Weather overcast and humid.

Not sure where to put this so posted a suggestion re a kit/equipment forum.
Walking yesterday and my GPS (Garmin ETrex) went through 3 pairs of AA rechargeable batteries in 7 hours. Normally 1 pair lasts about 5 hours.
The batteries were fully charged and I had 2 different types as well (took a set from my camera as visibility was so poor that there was no chance of neeeding the camera) so I don't think they were faulty. Another walker had the same problem as well.
Conditions were wet, very overcast (misty) and cool. All we could think of is that the GPS works harder in cloudy weather searching for a satellite signal. Does that make sense?