[azazel1024]

Lithium Ion battery life is limited by overall age of the battery plus total energy used from the battery (IE number of recharge cycles). Discharging a Lithium Ion battery fully doesn't really damage it. The anode/cathode chemistry isn't like a lead acid battery, where it is physically damaged by a deep discharge. Its the total amount of energy pushed through it, age and rapidity of charging.

So if the cells in it are rated for 500 charge cycles, you could fully discharge it and charge it 500 times, or you could discharge it to 90% and charge it back to 100% 5,000 times.

For age, a lithium ion battery will last longer if stored in cold conditions and interestingly it will last longer if kept at approximately 70% charge level. IIRC from reading up on them a couple of years ago, average cell life for common chemistries is about 7 years before capacity reduces below I think it is 50% of new capacity, but if stored at 70% charge perpetually (how you'd manage that, I don't know) you could squeeze rougly 10-20% more cell life out of it (storing it at 0% charge reduces life over storing at 100% charge).

Also charging a lithium ion battery quickly isn't too big of a deal with current chemistries, but once capacity gets close to max, damage can start to occur if you are charging quickly. Its why a lot of devices will allow rapid charging for about the first 80-90% of the cell capacity, and then slows down charging dramatically for the last 10-20% of capacity (example iPad 2 will charge from 0% to 90% in about 3hrs off a 10w wall charger, but then takes about a full hour to go from 90% to 100%).

This in part by way of saying, at least with an eink reader, unless you are planning on some seriously heavy use, the battery is probably going to start failing from age rather than any kind of deep discharge issues or even overuse. Most LiIon batteries can last upwards of 500 charges before they see significant reduction in charge capacity. At even 2 full charges a month, that is 20 years before use would result in serious reduction in capacity, so even if deep discharge reduced the battery life in half, that gets you 10 years of use (old age will reduce it long before then). Odds are good we/you will get 4-6 years of good battery life out of the device, pretty much no matter the usage scenario before you start to notice a decent reduction in battery life.

Since yesterday afternoon I've had the nook ST "turn off" I think 3 more times now after waking it and reading about 30-60 seconds. Twice last night and once first thing this morning. Both times I waited about 20-30 seconds and hit the power button, booted right up. First time last night it told me it has 8% charge when it booted, and then about a minute later it was at 49%. The second time it didn't give me a charge warning when it booted and just told me 48% charge when I checked in settings. This morning it also didn't give me a charge warning when it booted and it says 47% charge in settings.

I am hoping this is just some kind of really bizzare learning it is doing. I also noticed that it only started occuring when capacity basically went below 50%. I want to try to get it down to roughly 20% before I charge it just on the off chance that there is some kind of learning going on, and that a cycle or two of doing that will fix it.

If the permenant behavior is that once charge gets below 50% it will randomly power off when waking from sleep, that is going to be annoying, but at least so far it boots right back up just about and doesn't give me any problems until it has been asleep for at least a couple of hours. Of course, Dopedangle, you are right, if that is the behavior I am just going to charge it every couple of weeks to keep the level above 50% in normal use so that it doesn't do this, as it is really annoying.

However, I am lazy and don't want to have to live with shipping this off and waiting for a refurb, so unless it gets worse or really just breaks, I am not going to go through the hassle of a warranty return as it is usable, but with an annoying quirk right now.