Landing Voltage for 2s Li Ion

For Li ion batteries and also for Lipo batteries the best voltage to land your fix wing would be 3.5v in each cell. So in total your overall voltage would be 7v. You could fly till each cell in the battery gets to 3v and your overall voltage will be 6v, but if your want to keep your battery healthy, you should probably land your fix wing at 3.5 v.

3.2 to 3.5 or 6.4 or 7.0 land at 3.0 to 3.2 it will come up a little bit win it sets a mins. buy .2 to .7 and it will be safe

LiIon can be very different. Is there any documentation available on the pack you bought?

Do you have a current meter on board?

Li Ion has a Range between FULL 4.2V (sometimes 4.1V) and EMPTY 2.5 V.

If you use this Range, you can exept the full Load of Capacity.

If you land on 3.5V/Cell, you will NOT have the full Load out of your Pack.

i`ll prefer to land on 3V/Cell with my 21700 4S1P 4500mAh Packs.

Check the specs for the specific LiIon cells youre using, they usually are rated up until 2.8V or 2.5V or similar, then for 2S just double (5V or 5.6V respectively)

Li-Ion cells Typically are able to be flown down to 3V Reliably, However you mentioned you use an O3 Air Unit, which usually performance drops drastically below 7.4V So you will need a

BEC in the 9-12 v range with at least 2 amps of power to keep it powered when flying your Li-ion down to 3V-3.2V.

"It can be powered by 2S to 6S voltage (7.4-26.4V). The O3 max power consumption is around 16W, drawing 1.6A at 10V, if you are powering it from a BEC, make sure it’s powerful enough."

Reference to Oscar Liang: https://oscarliang.com/dji-o3-air-unit-fpv-goggles-2/#:~:text=The%20O3%20Air%20Unit%20has,(7.4-26.4V).