I'm flying a GEPRC Crocodile Baby 4 LR HD, cruising around the park. I get around 16 minutes with a Tattu 4s 1550mAh lipo. Super happy with this!

Then I tried the following 18650 li-ion batteries and only got around 12 minutes:
GEPRC 3000mAh
Auline 2600mAh
Molicel 2600mAh 35A (home made)

I land when the average cell voltage reads 3.5v in the OSD. My charger puts back around 1100-1300mAh.

I know li-ion voltage recovers a bit once you land. Should I fly it down a little lower? Is there some setting I can tweak in Betaflight to help with li-ion flight times?

Hoping for some warmer weather in Wisconsin to get back out there!

Hi mblaide,

First, the 16 minutes is pretty good Fly Time on a LiPo battery. 
What is the All Up Weight including the 4S 1550 lipo  ??

You should be able to drain an 18650 pack down to 2.5 volts per cell.  Are the 18650 packs 4S ??

You might consider trying a 3S 18650 pack and drain it down to 2.5 volts per cell. That would be 7.5 volts for the pack.
Some FCs have a low voltage cutoff, so you might not get all the way down to 2.5 volts per cell, but that is the goal. 

As a reference, a Tattu R-Line 4S 1550 pack has 22.94 Watt Hours (wH) of energy and weighs about 181 grams.
A 3 cell 18650 3000 mAh pack has 33.30 Watt Hours of energy and weighs about 150 grams.

The higher energy pack should fly longer even when drained to the same cut off voltage. However, the 3S 18650
pack can be drained lower which should provide even a little bit more Fly Time. Plus the 3S 18650 pack is a little
lighter than the 4S 1550 LiPo. That is the mathematics of it, so it would be interesting to see if that proves out
in actual practice. All, you need is a 3S 18650 pack to test. I would check the time when the pack is at 3.5 volts
per cell, but keep flying until you draw it down to 2.5 volts per cell or as close as you can get.  

I have not personally tested the combination, but it would be interesting to see your results. I am presently
gathering data on battery performances and comparisons.

My money says that a 3S 18650 pack will get you over 20 minutes. 

If you haven't done so already, you might take a look at My Parts Guide <--- click to download.


I am originally from Illinois, but now live in Florida where the weather is much better.

(27-Mar-2022, 01:30 PM)iFly4rotors Wrote: Hi mblaide,

First, the 16 minutes is pretty good Fly Time on a LiPo battery. 
What is the All Up Weight including the 4S 1550 lipo  ??

You should be able to drain an 18650 pack down to 2.5 volts per cell.  Are the 18650 packs 4S ??

You might consider trying a 3S 18650 pack and drain it down to 2.5 volts per cell. That would be 7.5 volts for the pack.
Some FCs have a low voltage cutoff, so you might not get all the way down to 2.5 volts per cell, but that is the goal. 

As a reference, a Tattu R-Line 4S 1550 pack has 22.94 Watt Hours (wH) of energy and weighs about 181 grams.
A 3 cell 18650 3000 mAh pack has 33.30 Watt Hours of energy and weighs about 150 grams.

The higher energy pack should fly longer even when drained to the same cut off voltage. However, the 3S 18650
pack can be drained lower which should provide even a little bit more Fly Time. Plus the 3S 18650 pack is a little
lighter than the 4S 1550 LiPo. That is the mathematics of it, so it would be interesting to see if that proves out
in actual practice. All, you need is a 3S 18650 pack to test. I would check the time when the pack is at 3.5 volts
per cell, but keep flying until you draw it down to 2.5 volts per cell or as close as you can get.  

I have not personally tested the combination, but it would be interesting to see your results. I am presently
gathering data on battery performances and comparisons.

My money says that a 3S 18650 pack will get you over 20 minutes. 

If you haven't done so already, you might take a look at My Parts Guide <--- click to download.


I am originally from Illinois, but now live in Florida where the weather is much better.

Hi iFly4rotos,

The AUW is 346g with the 1550 lipo and 375g with the 4s li-ion packs. I was unaware of the 2.5v cutoff for li-ion packs. This will give me something to test when the temps increase. We had a warm spell here last weekend (60s) but now we're back below freezing.

Thanks for the help!

You might also try a 3S 18650 pack. It will be about 50 grams lighter and provide more energy (wH)
than the 4S 1550 LiPo. Weight makes a difference. Lighten the weight and increase the energy.

There is the point of diminishing returns where bigger does not get you more Fly Time due to 
the increase in weight. 

I am interested to know your results. I am especially curious about how the 3S 18650 pack
compares to the 4S 18650 pack.  

Please continue to post your results as you try different battery packs.

Thanks, iFly

(27-Mar-2022, 03:00 PM)iFly4rotors Wrote: You might also try a 3S 18650 pack. It will be about 50 grams lighter and provide more energy (wH)
than the 4S 1550 LiPo. Weight makes a difference. Lighten the weight and increase the energy.

There is the point of diminishing returns where bigger does not get you more Fly Time due to 
the increase in weight. 

I am interested to know your results. I am especially curious about how the 3S 18650 pack
compares to the 4S 18650 pack.  

Please continue to post your results as you try different battery packs.

Thanks, iFly

I think I have a couple of Molicels left to put a 3S together. Then I can compare to the 4s Molicel I built.

Regards

Li-ion packs are for slow cruising.
Becareful. Maybe use throttle limit.

Batteries suffer when its freezing.
The 3S should give very good flight time.
You should not go down below 3.0V per cell... only like 1% left anyway.