The battery charging behavior of webOS devices is something that has interested me for a while because I'm a bit OCD about maintaining my battery life, especially with the non-replaceable (without a crazy amount of work) battery in the TouchPad.
I'm curious about your theory regarding the new charging algorithms based on the A6 chip in the TouchPad versus the behavior in the older devices. You have stated that you feel better about leaving your TouchPad on the touchstone all the time because it seems to switch over to being powered only by the charger after the battery is full. I would like to believe this is true, but I'm wondering if the ~15 mA drain we see isn't just the result of the charging circuit taking just what it needs while running that current through the battery. In other words, I think the TouchPad should still be running off the battery, but now the charger is supplying almost exactly what is need by the TouchPad to maintain the battery at 100% charge. It is true, as you mentioned elsewhere, that it is possible for a device can run straight from the charger without using the battery because it is possible to swap a battery while the device is plugged in. However, there is only a short window during which you can swap the battery before the device shuts down completely. My guess for why this behavior exists is that the battery is used to condition the power signal coming from the charger, much like a UPS for a computer, and Palm didn't want to trust the signal coming straight from the charger. That is just a theory, of course.
Anyhow, my concern is that even though there is only a small overall negative current for the battery in the TouchPad at 100% when it is plugged in or on the touchstone, the battery is actually still being used to power the device while it is simultaneously being charged at exactly the correct rate to maintain 100% charge.
From reading a number of articles on battery life and charging, I have come to understand that the biggest enemies of battery life in a Li-Ion batter are heat, deep discharges, high voltages (such as those reached at and beyond 100% charge during the trickle charge phase), just plain usage, and aging (an unused Li-ion battery will go bad over time).
If the TouchPad maintains the full 4.2 V on the battery cells the whole time it is charging at 100%, then I think this is probably worse for battery life than the 95-100% discharge cycle seen in the older devices UNLESS it is true that the TouchPad really isn't using the battery at all in this scenario. The good thing about the 95-100% discharge cycle in my Pre 2 is that the battery is allowed to drop to a lower voltage state once 100% charge has been reached.
I also still have concerns over the heat buildup in my Pre 2 as a result of using the touchstone as heat is probably the #1 enemy of Li-ion batteries, but I suppose that is a topic for another thread.
As far as I can tell, an ideal (but unrealistic) usage case for a Li-ion battery is to keep it below 30 C while using it from 95% down to maybe 90%, turning off as many things that use the battery as possible while charging it back up to 95%, and repeating this cycle. This would avoid excessive heat, deep discharging, and higher voltages.
I wish that webOS gave us an option to only charge to 4.1 V rather than the full 4.2 V because this should, in theory, extend battery life at the cost of some battery run time. I know that some laptops have such an option where you can choose either overall battery life longevity or maximum battery run time. Then I would be much less concerned about leaving my device on the touchstone all the time. Right now I generally pull it off once it reaches 100% in order to avoid the higher voltages that come with the trickle charge portion of the charging curve, not to mention the heat buildup that seems to be much more of an issue with the webOS phones than the TouchPad.
Sorry for the really long post. What do you think about all that?