Hi Mike,
Here is a recent anecdote that may be useful.
We purchased two new identical Toshiba Satellite laptops in June 2009.
Both were typically run off batteries a couple of hours a day.
Both were used in the same environment with WiFi connectivity.
The power settings on both machines were set identically so they would not
automatically suspend themselves.
Machine A, when not in use, was typically plugged back into its AC adapter.
At least once per month, as per the recommendation that comes with the PDF Toshiba
User's Manual with the machine, it was operated off battery power until the
battery was depleted and then it was plugged back into the AC to completely
recharge. When left idle, this particular machine was typically left operating off AC
with its lid open so it could be used at a moment's notice.
Machine B was typically charged fully and then not re-charged until the battery
was depleted. When not in use, its lid was closed and it was allowed to suspend itself.
After approximately 18 months, the battery run time on Machine A had dropped to
approx. 10 minutes. On machine B, the battery run time on Machine B had dropped
to approx. 30 minutes.
This was consistent with a previous generation (circa 2001) Toshiba laptops
we used.
Given the minimal sample size, perhaps not much can be reliably read from this
except for the fact that for these two machines, after about a year, the batteries
would be regarded by most users as being toward the end of their practical usefulness.
As you can appreciate, the underlying technology in laptops has followed
Moore's Law.
As speeds increase, so do their power requirements and portable systems designers
are engaged in a relentless challenge to achieve the highest speeds, when required,
and yet to minimize the overall power consumption of their devices. Such
power/speed trade offs take place from everywhere down to the gate level all
the way up to the operating system. However, despite advances in battery
technology, it has not maintained the same dizzying pace as semiconductor
technology and this raises the bar for laptop designers even further.
As has been noted, the batteries that ship with many laptops often have
lower mAh capacities to keep the price lower.
