[JASJAR, XDA Exec, MDA Pro ROM Development] EvilJogga:
As this is my first post here:

Hi everybody :)

I recently bought three Universals (yes, it was on accident!), two of them coming with a spare battery, which gave me five batteries. Unfortunately, only two of them worked well, the other three were somewhere between half-dead and dead.

The corrupted batteries I had weren't just decalibrated and behaved the same in every one of the three devices. Taping the capacity monitoring pin made no difference.

The protection mechanism of the batteries

At least the original ones have a built in safe circuit, preventing them from being drained to death. It seems to work quite simple, by just cutting the connection between contact plates and actual cells if the cell voltage drops below a certain amount.

My experimental setup with the dead battery (shutting off at >>90%) was easy. An usual digital voltage meter and an 8 Ohm resistor, draining about as much current as the uni does at full load. When the Uni shut down, the protection circuit hadn't cut off the cells already, there was still a measurable voltage left. In fact, the voltage was very high, somewhere above 4V, as you'd imagine from a battery at 90% :D

So putting the resistor at the battery and watching the voltage showed, that there was a massive drop under load. In seconds the voltage was below 3V. At this point the Uni should shut off very likely. Keeping the resistor connected lead to the described cut off, the voltage at the contacts was zero.

Putting the battery back in and connecting the uni to a charger for just some seconds reactivated the contact plates, the battery was back alive. After some moments of waiting with 4,xV again!

Why is this happening?

My explanation is quite simple. Due to age and charge\discharge habits, the inner resistance of the cells gets higher. This is part of ususal wear, but wrong handling seems to drastically increase this.

As some people may not know, the battery itself is to be seen as a second resistor besides the universal, of course both are connected serially. The voltages dropped at a resistor in an electrical circuit follow the same ratio as the resistors' resistances. This means if the inner resistance of the battery raises, the voltage provided to the uni decreases enormuosly under load. This can easily been experienced by turning on backlight and wifi with a half dead battery. After some seconds the Screen goes black and the device has crashed.

My conclusion

The increase of inner resistance as a result of aging is irreversible, but the increase generated by mishandling seems to be reversible, t least partly, by cycling.

If a battery dies below 30%, load it to 100%, then drain it at full load until it shuts down, wait some minutes, so the device will boot up again, then disable backlight, wifi etc and wait until the device crashes again due to low battery. If it isnt drained below ten percent, drain it further by using an LED.

Then reload it with the ac charger and do this again some times. Most likely the battery will now be drainable much further. This straightened out two of the batteries for me :)

If the battery dies above 30%, it is most likely quite dead already. Intense cycling will improve battery life maybe a bit, but cannot revert the inner decay. It is worth a try, but you better make friends with the expense for a new one.

If the battery dies above 70%, you will have problems draining the battery, even with an LED. Even with several attempts I couldn't restore none of the batteries above shutting down at ~60%.

Try taping the monitor pin, as this will not disable any safe mechanism inside the battery (i can only speak for original ones), and maybe you have better luck than I had.

In future, consider to do one or two intense cycles from time to time. At least for the various LiIon andLiPo batteries I have around here that helped keeping them alive far beyond two years.