This information was written for the Autel X-Star by Heath. He had written a whole document on the XSP's battery and had it approved by Autel. This is just one section of the PDF file but I think you can use it for reference on the EVO.
Another possible "critical drop" cause**...The battery's total mAh capacity is calculated
at each charge.This capacity is also used in the calculation of battery percent remaining.
As it charges, it counts the mAh going in. Once the charge finishes, it averages the new
count with the history of past counts. This is why Autel recommends you run the battery
down to 7% every 20 charges, at least. Now, if you are one of those who tends to bring
it in before the battery warning often, you may want to do this more often...Remember,
the total mAh capacity is based on the average of energy it takes to recharge to full.
Continuous partial discharging (bringing it in early) will cause the total mAh capcity to
fall, which is one thing that causes the sudden percentage drop and **critical land**.
My recommendation is to periodically bring the quad in close when it approaches
warning percentage to stop RTH from kicking in, then before critical percentage, bring it
low, perhaps 5 feet off the ground. When it reaches critical, hold the stick up to keep the
quad aloft until perhaps 5%, then let it land. It will force land around 3% no matter what.
This means on next charge, the count will be high, helping to recover the total mAh
capacity count.
