max charging current through 18650 and holder

I am not able to charge with much more than 1.5A before charger goes into CV.

What are your max charging current in CC mode and what kind of holder/connection are you using? I think it should be higher that what I am getting, I suspect protective circuit or battery holder might be the bottleneck.

It’s way less that I can push in with my RC lipos.

I do not experiment with maximum charge current, but I can see from testing 2A chargers that it takes some time before CV phase is reached:

Of course, if you use cheap batteries or protected batteries they will have higher internal resistance and the voltage will raise faster.

The Lipos for RC use is often designed for fast charge, this it not the case with high capacity 18650.

What battery was it and what’s the charge state when started charging?

I can generally do 2A with no issues with a lot of my batteries, normally halfway drained (but I almost never charge that fast unless need it quick).

Empty was the battery. Any one of mine: trustfire, Sanyo, Panasonic.

How are you connecting to the battery? What holder? Magnets?

edit: trustfire 2400mAh, sanyo 2600mAh, Panasonic 3400mAh, all protected.
holder is the crappy thin wire 4x holder from dx, charging only one battery at a time, using SkyRc Imax B8+ charger.
I will try perhaps to remove protection from one of the batteries to see if it is introducing the voltage drop.

I use cheap holders too, but soldered the end of the spring directly to the wires (so current bypass the spring).

I also rigged another line out of of my Imax B6, this is directly soldered onto the mainboard. I use 2.5mm^2 wires (AWG14/16? Not sure the conversion).

Basically I have fully soldered connection end to end. Helps in testing/fully charging batteries without voltage drop on connections.