Guidance on the manufacturers website says to expect 2hrs 30mins use with a full charge, depending on settings. I'm not naive, I'm sure this is the optimum they got in testing using the lowest intensity setting, whereas I'm using a middle range setting (4 of a possible 7 intensity settings). I'm consistently getting 1hr 35mins, 1hr 40mins at most. The manufacturer says this is within their expected parameters, but I expected more. Am I being unreasonable to expect it to last longer than this?