I hope this is the right place to post it.

I've just built my own 4s battery based on Liitokala 3.7V 3000mAh 18650 VTC6  cells. No actual  flying done just yet but a hoover test. I didn't time it but for sure lasted longer than my 1500Mha lipos.

What I noticed though was that the drone would disconnect from my controller and the goggles when heavy on throttle at the end of the battery .

My question is - would it be safer to run 6s battery to make sure DJI unit gets its 9v constantly, even when the battery is being close to its lowest voltage.

Also is discharging to 2.5v safe?

It might help butvthats a big weight penalty for another 2 cells. Voltage sag is an issue with lithium ion, I like to up it 1s over what I'd run for a lipo where practoval but youl still experience voltage sag and it can be pretty extreme at the end.

These don't have a very high c rating, usually about 1.5c recommended discharge rate. That should equate to a 45 minute flight time and no one's really achieving that for 4". So can you go safely to 2.5v? Maybe. Lots of people run to 3.1 volts or so but the full rated capacity is generally to 2.5v and is considered safe. But only when they are not being discharged wildly fast like we do. I do it often enough but I'm hardly maintaining flight at that point I'm just doing a low creep back keeping the amps as low as possible.

The larger size 21700 have a much higher discharge rate I haven't tried any yet but aside from 4" the's will probably be all that I buy going forward for 5" and up if they prove to perform better for multirotors.

I never thought of 5s but I like the idea. I guess it would allow for a good balance between the weight and the minimum voltage allowing the airunit to stay on when the battery fully discharged.

Also the cells discharge is rated as 30a, am I right in saying that the discharge rate would be 1c?

5s is a pain to find a nice way to orient them but it does help the voltage sag but my 7" handles the weight penalty fairly well. I've never tried a 5s on a 5" that might be iffy with a 250g battery pack.

I'm not familiar with those batteries but here's an interesting article worth a read. The part about identifying the cheap or fake 18650's might make you question rated amps unless you trust your source. These are only capable with current technology of about 3500mah but some of the off brand cells are sold rated much higher than that. I buy from 18650 Canada, they do sell off brand and the last batch I received they batch tested and rated as 2500mah and suggested 5A max if I remember correctly. I'd found them online elsewhere as 3500 and 40A discharge. Vape store cells are notorious bad and overpriced, at least in my area.

https://www.google.com/amp/s/www.makeuse...ttery/amp/

That would be 10c for 30A discharge rate.

Funny, I was just looking to lion last night. But I would need a 6s. The weight and cost seams not worth it. Maybe in a couple of years when 6s is more prevalent.