For what it's worth, this is the best li-po battery use page on the net that I know of:

http://www.batteryuniversity.com/parttwo-34.htm

Eg "Batteries with fuel gauge should be calibrated by applying a deliberate full discharge once every 30 charges. Running the pack down in the equipment does this. If ignored, the fuel gauge will become increasingly less accurate and in some cases cut off the device prematurely."

That has been discussed before. AFAIK, and experience backs this up, the above applies mostly to laptop batteries, which are stacked batteries (that is, cells not only in parallel but in series too). I'm almost 100% certain that there's no such fuel gauge in the kind of batteries used in the NITs and similar devices, instead there's a simple voltage meter in the device which measures the current voltage and calculates everything else from there.

For the record, my N800 is from January 2007 and the battery metering works exactly as it's always done, and I avoid discharging the battery like the plague (it's happened by accident maybe 4 times).

On this topic, what is a good rule of thumb for when to charge the battery?
For example, I avoid "topping up" the battery in my laptop for small amounts, as I have been told from a few sources that its lifetime is affected by charge / discharge cycles. Does the same idea apply to the batteries used in the N800 and N810, or are we a bit safer just popping it in when convenient

The article is quite informative there, and it seems to suggest no need to worry, but I am not much of a battery person.

One thing is for certain: These batteries are much easier to come by than the insanely specific laptop ones.

Don't be afraid of 'topping up' the battery whenever you get the chance. What reduces the lifetime and capacity of your NIT battery (or any other 2/3-cell, non-stacked lithium-ion or lithium-polymer batteries used in small mobile devices) is deep discharges.

I've had my N800 since January 2007 and the battery is as new. I charge it whenever I can and avoid deep discharges as the plague, although that's happened accidentally a few times due to some applications running wild with the CPU overnight. I've also seen a _single_ deep discharge of my mobile phone completely destroy the battery - it went from 3 weeks to 2 days capacity.

Laptops are in a different situation for 2 main reasons:

• Their batteries are stacked, that is, series- as well as parallel connections of cells due to much higher voltage (series connection is needed for that), which means that they'll usually need some initial discharge/charge cycles to 'level out' cell differences, and they may also have a 'fuel gauge' which needs the occasional discharge for recalibration (see the OP's post).
• The more important difference is that laptops are hot inside, and lithium batteries don't like to be 100% charged when they are hot - it kills the lifetime of the battery. Laptops that always stay on mains will typically end up with useless batteries after a year or so. This does _not_ apply to cooler devices like the N800/N810 or mobile phones, they behave very differently in this respect.

So, in short - think like a soldier! (try to get some sleep whenever you can, you never know when the next possibility comes up.. just replace 'sleep' with 'charge')

thanks for the thread as I was not aware the design of the LiPoly batteries was parallel not series.

It was always my understanding that LiIon of all sorts do work best when "topped off", as mentioned vs. repeated full discharges. Even laptop batteries last longer and retain more capacity (I think?) when used in this fashion.

Question about LiPoly batteries. Are they like their laptop counter parts in that when stored for extended periods it's best to leave them discharged to around 40%-ish? I ask because if a person has two batteries or more for theit NIT it would help to know what soort of rotation cycle will get the best useful lifespan (not runtime) from the batteries.

Correct. It's a bit more complicated than that (and i don't know all the details) but no internal gauge and smartness.

For laptops there's a complication in that they're much hotter inside, and Li-Ion batteries don't like heat when they're 100% charged up - it destroys the lifetime of the battery. Laptops that always stay on the mains tend to end up with useless batteries after only a year or so. Certainly that's happened with every single laptop here at work, ever. The only laptops that still have useable batteries are those that either are mostly on the road, or are taken care of (i.e. not staying on the mains all the time). There are some (very few though) laptops on the market which can be set to not charge to more than 80% while on the mains, if you want a 100% charge before you go on the read you have to tell it so. This feature is meant to handle this problem with 100% charge and high temperature.

That's my understanding, from reading up on batteryuniversity.com. I have a few extra batteries for my mobile devices, I charge them to 40-50% and I keep them at 4-6 degrees C in the fridge.

That's interesting about laptops with an 80% feature; IMHO, the thing to do with a laptop (not having such a feature) used as a desktop is just pull the battery and toss it in a desk drawer; when you want to move, slap it in, and go; when you get back, plug into mains, wait till the battery is charged, then pull it and toss back in the drawer. Of course, my present (ancient, NiMH powered) laptop has battery life about 30-40% original for the good battery, and about 20 minutes of the old one; I ordered some new cells, but when I get around to putting them in, it's becoming a primarily in-car machine... I'm not real sure what the best solution is for that.

For Li-ions, I think it's best to leave them at zero, from a battery-degradation perspective; but you can't do that, because if they drop below zero, you can't safely resurrect them at all. Since there are no internal electronics to drain power, 20-30% should be doable for N800 (and most cell phone) batteries, and is preferable to 40-50%, but one can always argue safe/sorry tradeoffs...

I do exactly that -- I remove the battery from the laptop while on mains. Not all the time, but often. It's still good for 3.5/5 of what it managed 3 years ago, some 3.5 hours.

What about partial charges? If you don't have time to charge the tablet to 100% is it best not to at all? I somehow got the idea it's a really bad idea to stop Lithium batteries charging before they're full.