I tried all the info available on the help sites to no avail - changed battery (twice), rebooted, cleaned it out etc etc . Nothing worked. Then one day in bright sunlight I realised I could see up the 30 pin socket and had a look. Lots of green crud - corrosion. Cleaned it out as best I could with a toothbrush, battery life went from three hours to eight immediately. Bought a new charging circuit board which incorporates the 30 pin socket for the princely sum of £3.75, fitted it, it is fiddly but doable with the video guides on youtube, and lo and behold all back to normal. Evidently moisture had got in there at some time and I suppose galvanic action had caused corrosion that allowed current leakage. Remove corrosion and bingo! Job's a good'un!