I am running one of my projects from two 2000mAh Lithium Ion batteries wired in parallel
I decided to let the battery run until it died, just once, to see how long it would last. It lasted 25.9 hours, and when I checked the voltage on them, they had gone down to 2.5V.
I've read in many places that Li-Ions should be 3.7V when full and 3.2V when empty, but I've never seen anything about 2.5V or anything lower than 3V for that matter. I have heard and seen people talk about "overdraining" a Li-Ion/Lipo, and that when it goes below 3V a microchip disconnects the battery to protect it from discharging too far.
In this case, my battery still works, and it is charging right now, I don't plan to run it down that low again, but if it were to happen again, is it a big problem? Could this effect the longevity/performance of the battery?