I am such a dunce... I never knew that you could actually turn off the WiFi on Jerry the Berry. As a result my battery has been draining faster than water down a plughole. Before actually being told that you have to turn it off to make the battery last I had to charge the thing 3 times since Saturday, which probably would have been more if I'd kept it on during the night as well. So now that I've turned it off, the battery is steady eddie.
Ahem, I need to think logically about these things in future.