I have just upgraded from a 2800 to a 3500. With the 2800 the battery life was about 5 hours and so I had to by a back-up battery for longer walks. When I purchased the 3500 I was assured by the sales person at MM that the back-up battery would fit both models. is this the case? Also what are people's experience of how long a fully charged battery will last on the 3500.
I have both of the units and the answer is no, the batteries are completely different. As for life expectancy it will vary depending upon usage but various users have reported between six and eight hours. The most I have had was seven hours but the battery was not completely exhausted.
Hope this helps