My understanding is as long as you are within a 3.4 to 3.6 threshold you are good. My hyperion has taken a 4S down to 13.6V before. Those chargers are very fickle about not going below a safe threshold. Max amps claims not to discharge below 3V. I would find anything thing near 3.2 to be unsafe. My experience with charging although I never record the numbers, is that 14.2 is sweet spot with the QC lipos unless anyone else has any other insight.
There is a capacitance effect to the battery that is going on its evident by the voltage discharge curve. Its sort of a negative logarithmic curve is more linear with lower decay as time T increases but will continue to decay at a slower rate. a good example of this is Andy's guide on page 4. http://rathergoodguides.com/RGG_documents/RGG to Comparing Certain LiPo Batteries 1-04 2013-04-12.pdf The red plot shows voltage. Notice it sags fairly fast then the decay is steady. This is because there is one essential element that failed to be mentioned. That is the internal capacitance of the battery. That is why it exhibits this behavior. As the resistance is increased due to load the battery is discharging faster and therefore reaches a point where it stabilizes. That is why the battery restores some of the voltage as some of the load is reduced ,as noticed in his plot because its the capacitance of the battery that is able recharge the internal capacitance. This not recharging the current but more so the static force of voltage. That is why you will rapid dip than stabilizes its the physics of the battery at play. The best way to imagine it is that you have several buckets of water with a drain tap and a hose connected to a larger water supply which we will suppose collapsible bag that will replenish it. The buckets are the capacitance of the battery cells. The collapsible bag is the rest of total charge of the battery the goal of the water is to try remain at a steady pressure. You pull from the battery, this would be like opening the drain cock and letting the water flow out while simultaneously turning on the hose to replenish the water. There will be an initial out rush of water flow that will be greater at first and will reach a steady state. Imagine its flowing into 8 empty hoses connected to 8 propelling sprinklers and that initial free volume of the hoses causes more to flow at first until it reaches a steady pressure. The replenishing source is slower than the water exiting the bucket. So the flow of water going out is more then the flow of the water going in. So the bucket will decrease its level eventually and will almost drain out supply bag completely if ran too long, i.e. a completely discharged battery. But, say you don't drain out the supply bag completely, just part of it. Then you close the drain i.e no longer pull current. Because the water going into it is not an infinite supply it fills the buckets back up to a new lower level. You will see the water rise back in, but it will never reach the level when it was fully charged, this is an example of the battery returning back to its resting state and now is at its lower charge state. Recharging the battery would be like putting water back into the bag then would trickle down until the max allowable pressure of the bags and buckets are equalized. Everything in nature wants to reach equilibrium. But over time these buckets shrink, they are made with some crappy material that does this, and can longer carry the same amount of water when they were new but the pressure will stabilize to same level it was before but now at a lower unit volume. This is degradation of the cells over time. They will reach the same potential however with less capacity and eventually run out quicker when the drain is opened again. Why are you pulling more current now? It could be possible that a motor maybe shorting out. Epoxy resin on the stators or wire wingdings might be degraded allowing for a fringe current to leak. Test each motor under load and note the total power pull from the entire system. If one motor causing the system to pull more than you may have found your culprit. My guess is a motor over a BL, because I think you would have blown a BL by now it were shorting. It doesn't take much to zap those out of commission. I only offer this as a suggestion if you are getting abnormal results with previous loads. I agree you should not be stressing the aircraft that much with a 5D and a nifty 50. Max you should maybe see 70 to 80 amps at hover depending on the battery voltage. If you are pulling 100 Amps in a no wind hover with a 5D/50mm then something is not right. One other thing to look for is to see if a motor maybe having a baring issue. You can sometimes tell by hand turning the props. If one motor looks like its wobbling or has a crunchy sound to it it could be exessive friction on the motor. Shaun