[HD2 General] motoi_bogdan:
well.. the idea originated from laptop battery tricks and some facts about the technical side of the problem.

If i try to simply put it, a laptop battery contains (beside the actual battery) a small pcb that has a charge/discharge controller and a eeprom memory chip (among others). The point of having these is also pretty simple. The battery actively communicates with the laptop via a i2c interface, so that the laptop always knows the state of the plugged in battery. The laptop itself can't measure the current or voltage of the battery and doesn't know it's capacity or composition. Instead the chips inside the battery does all this work and reports it to the laptop. That's how the laptop knows when you plug a different capacity battery or other things. The percentage of power remaining is measured by the chip inside the battery and stored in a volatile memory also contained on the small pcm inside. This memory can be accesed by the laptop and from there, it will display you the remaining power left (in percents %). This is updated as long as there is any notable difference from what the chip measures from the battery cells and what was the last measurement made. So.. what would happen if you would charge the battery to 100% full, then disassemble it, remove the 100% charged cells and replace them with 50% charged ones.

When you would start the laptop next time, it will STILL display 100% charge, the last measurement, and will assume this state is valid for the cells. When the physical batteries will drop the charge level with 1% the laptop would display 99%. So around 50% displayed the batteries will actually be empty. When you charge them back, the laptop would start from 50% and go back to 100%. The actual batteries would get only 50% energy, so they won't get fully charged, therefore you get less battery life.

Of course, this is a very exagerated scenario, but in practice, sometimes small errors can occur, when the physical level of the batteries is a bit different to what the battery controller recorded. In this case, a full discharge then recharge can help to correct this issues (but only if you're talking about couple percents - not more).

But... when we're talking about phones, things are quite different. The communication algorithm between the battery and phone is more simpler and the battery itself doesn't know it's charge state. The phone will actively probe the battery in order to update it's status. So, if i remove the battery and drain it somehow, the phone will display it's correct physical charge next time i plug it in. This is possible because a phone battery and the phone itself is simpler by design then a laptop for example.

So why laptops used such complicated charge algorithms? Mainly because 2 reasons. One because laptop batteries are dangerous things. If improperly charged or damaged they CAN explode. If the cells are damaged, overcharged or the temperature is high, the controller chip will change the state of the eeprom memory so that the laptop and it's OS to see that the battery was damaged/empty and shutdown at once. The other reasons is quite commercial based. The charge controller counts each charge cycle and stores it in that eeprom memory. So if the manufacturer specified a specific number for the charge cycles, when this number is reached, the controller will simply rewrite the eeprom and state that the battery is "dead". So.. go get a new one.

I disassembled many batteries and among "dead" ones, i found many cases where the cells were actually in pretty good shape and functional. I measured cells with more then half the original design capacity still available, but the battery pack was reported as being "dead".

So back to hd2. As i've stated, phones use simpler charge/discharge algorithms. The better part is that they are more simplistic and efficient at measuring the actual physical state of the battery. So, a calibration isn't required like on some laptops.

However, sometimes is good to have a full discharge/recharge cycle. This being because of the chemistry of such a battery. It won't do miracles, it won't make the battery last longer on a charge but it could prolong overall battery life. Lithium is a very reactive element, a deep discharge about once a month will help reduce the effects of naturally occuring oxidation of such materials in an electrolytic compound.