Input/ advice needed (2x 18650 mech box with USB charger)

[iTiger]

Hello I could use some help with my mech box project I'm planning.
I have drawn up a diagram that should work but figured I'd post here for others to confirm or tell me what needs to change. I had no luck finding good info on adding a charger so this is best guess from past electrical work.

For the most part I'm planning a basic dual 18650 mech box mod but with one twist; an onboard micro USB charger.
I'm on the go a lot and that's what started me wanting a dual battery box so I borrowed one from a friend and found I still killed the batteries before I could get to a proper charger so I was thinking about adding an onboard charger and started looking at options.

For the most part I've acquired no parts for this build but I do already have the circuit board that is a micro USB charger that charges 14000/18000/26000 batteries 4.2V.
I'm working on wiring up parallel 18650 to test the charging abilities but currently testing charging on a single 18650.

Anyway I know there are boxes out there or coming out soon with the built in charger but I'd like to build to taste and have a one of a kind setup.

Thanks for any help.

 

[iTiger]

Small update: tested charging a single 18650 with the charging chip I plan to use for this project.
The battery is showing full charged at 4.22V and the max output of the charger was 4.23V. As far as I could tell it did step charging (charged at ~3.6V then ~3.7V and so on until full charged.

Next will be to wire up a pair of batteries in parallel for charging to test the abilities of the charger chip.

 

[iTiger]

Really would like to know if this will be the correct wiring setup before I order parts but I'll just hold out for a little while to see if anybody chimes in.

Also wanted to add my test of charging 2 18650 batteries in parallel worked very well and showed fully charged end voltage of 4.26V with charging chip max reading at 4.27V just before charging stopped.
So as long as I wire this up correctly in a mech box I should have a nice setup.

 

[drmarble]

Looks like it should work fine. You might want to put a 15 amp fuse on each positive lead, one per battery. That will save you if you put one battery in backwards. If you will never do that, skip the fuses.

 

[iTiger]

Thanks. I thought about the fuses but not worried about it. May do it depending how I'm feeling when I start ordering stuff when I get paid.

I did have a old coworker suggest adding a cutoff switch so it can't be fired while charging. I like this idea and may see about adding that to my plans because I know that charger would most likely die fast if I tried to vape while charging. Because in the little info that came with it it says do not discharge batteries while charging.