As explained earlier one of the benchmarks missing in this lineup has to be MobileMark. Since we did not have the benchmark present at the time we tried to measure the battery life manually, which is probably the most accurate anyway but not entirely consistent. This is not an exact science but we were able to record the time you can use the notebook under certain conditions. The recorded times are rounded to the nearest hour. Battery life was tested with the notebook in regular power saving mode and not in performance mode which means the CPU and so forth are not running at full speed and the screen is not at its brightest setting.
Using simple programs such as Microsoft Office, some games, photo editing software and other various small programs we mimicked day to day work on the notebook and measured the lifespan of the internal battery. In this case the battery life span came down to roughly four hours with day to day usage.
If you use the notebook for heavy duty gaming or rendering of any kind the battery life is shortened to about three hours max and that is being generous.
When casually reading documents or eBooks, the life span of the battery increases to about five hours. For a business user just reading e-mail, the battery life is quite good and while it's not the best out there, it is one of the better notebook models.
Luckily battery charging is quicker and easier then draining it. Dell has incorporated the ExpressCharge technique by which a 6-cell battery loads to 80% charge in one hour and 100% charge in 2 hours. This D820 houses a 9-cell battery so it takes a little longer then an hour to reach the same levels, but it is still impressive.