[Brassman]

Hello my quad will cut off the motors compleatly at 3.7 volts. Im running dys bl10a ESCs wich have blheli firmware from the factory. is it possible that the escs have low voltage cutoff or is it the cc3d? wierd thing is that the esc restart with the beaps when it happens and I can start it right up without having to armed it again and fly for a couple of seconds if I just go slow on the throttle... anyone have simular experience or know how to solv this. the battery is a 800mah 2s old lipo that is a little swollen and the same thing happens but even worse on my other two 2s 1000mah batterys that are alot more swollen. I got twice the flightime from the 800mah compared to the 1000. Mabey its just the batterys that are too far gone. Im waiting on a battery shipment 3S 1800mah but I havent recieved them yet.
Thanks

[TheOtherCliff]

3.7volts is actually very low.  If it measures 3.7 volts per cell after flight, you have completely drained the battery.

BLHeli and SimonK firmware don't do low voltage cutoff by default build option, so what is happening is that you are draining the battery so low that either the FC or the CPU in the ESC resets due to low voltage.  This is not good for your battery.

Buy several of these beeper alarms and set them for say 3.6 volts alarm and always use them for every flight.
http://www.ebay.com/sch/i.html?_odkw=8+s+lipo+alarm

[Mateusz]

You must measure your battery voltage per cell. If total voltage for 2S battery is only 3.7, that's like 1.85V per cell, your battery is totally dead. I am surprised you managed to charge it back.
Charging swollen battery you risk fire (or self injury if it explodes), pressure that builds up may damage the pack and if air mixes with the content you have fire. Also if you treat your batteries that bad, their internal resistance increase and they become harder to charge. With the increased resistance, charging them at the same rate accumulates heat which again might set a fire.

If you fly, and drain battery to 3.7V per cell, land, disconnect battery, it should jump back to 3.8V per cell, which is around perfect storage voltage (7.6V total voltage for 2S) given that your battery is balanced. If you drain your battery in flight to 3.6 per cell or lower it won't go back to 3.8 in rest, and you need to recharge them for storage.

Generally voltage per cell under load is different from the one in rest. Good voltage for storing is 3.8V in rest per cell, and battery should never have it's cells below that voltage for longer period. Flying to 3.7V per cell is ok, as good battery should jump back to 3.8 after disconnecting it, but it's always good to check and recharge if needed.

I use this http://www.banggood.com/Wholesale-1S-8S-Li-po-Battery-Voltage-Tester-Checker-Indicator-Monitor-Buzzer-Alarm-p-26049.html which shows voltage per cell and beeps when battery gets low, but there are also other sensors or ways to prevent draining battery below safe voltage.

[Brassman]

So becouse the battery is under load when this happens the voltage is accually way under 3.7 and when the motors stops the battery voltage goes up to 3.7 again, right? and becouse its only a 2s battery the total voltage drops beyond the voltage recuired to power the fc. just a note Im running a 5 volt 3 amp bec to power the fc but i dont think this makes any differance to this problem. Im gonna get some low voltage buzzers on my next order, its already in my wishlist I have a feeling the problem will vanish with the use of 3S batterys becouse of the higher voltage. lets say I got 2 volts per cell under load, then I will have 6 volts under load with the 3 cell pack.
Thanks for your help man!

[Brassman]

the total voltage was 7.4...it was 3.7 per cell. I dont treat hem bad really they are over 5 years old have alot of cycles on them. Im gonna dispose of my two 1000mah packs, they served me well and they are finished....Im gonna cut the leads of them and put them in a bucket of water and salt mixture.
thanks for your replay man