No doubt - fail-safes have to be set specific to the mission. For battery fail-safes, you have to have enough juice to get home - different for a mission around a lake versus doing auto-tune over an open field.
Today I was maybe a minute or two short of flight time to complete an auto-tune due to a battery fail-safe. With an 8Ah battery, I have 21.6V and 1400mAh reserve set for battery failsafe. The failsafe reached the reserve limit - with still at 22.05V.
While I’d increase these limits if I were flying over water or trees, it seemed to work out fine for an auto-tune flight over an open field close in to my base. Especially since the fail-safe action is to just land.
Sorting through this, I was wondering if anyone might have some general rules of thumb to share on setting battery fail-safes.
Have you ever heard the joke that there are two types of people: those who stop at the gas station any time they go below ¾ tanks, and those who stop after the low-fuel light has been on for a day or two? (And they are usually married to each other)
I am very much in the former. So I fly watching my battery cell voltage. I will adjust my flight so my in flight voltage never drops below 3.55v, ideally landing closer to 3.60. This usually leaves my battery resting cell voltage well over 3.7 so I know I’m not abusing my batteries. Because I know how neurotic I am about watching battery levels I actually run without battery failsafes and set my battery warning levels at 3.65 or even 3.60v. This process may not be recommended for all people. For setups I build for other people I configure the failsafes with the default values like those used in the initial configuration setup tool.
I’ve also setup all my gear to work by cell voltage, that way no matter what type of battery I fly (3S, 4S, 6S) I don’t have to change my process or try to do math in my head during flight.
Your mileage may vary.