My project consist of 3 solar panels (6 V - 1 W each) that will charge 18650 li-ion batteries and with a step-up converter the batteries will charge electronic devices through usb.
To charge the batteries I'll use this module
As step-up module this one
The batteries will be connected in parallel as the 3 solar panels.
i have almost no experience with li-ion batteries

My questions are:
- can I charge multiple batteries in parallel with only one charging module?
- do I need a voltage divider or a voltage regulator to lower the voltage of the solar panels from 6 V to 5 V for the charging module?

p.s. I'm new in this forum, sorry for any mistakes

 

My questions are:
- can I charge multiple batteries in parallel with only one charging module?

You can, but it's not ideal. It's hard to ensure the cells in parallel are very nearly identical. Manufacturers do it by using tight specifications and maybe even cell-matching procedures. Once the cells fall out of sameness, the controller can't protect them both at the same time. For a DIY project that is not terribly critical, you can probably live with this.

- do I need a voltage divider or a voltage regulator to lower the voltage of the solar panels from 6 V to 5 V for the charging module?

First let me point out that there are charge controllers designed specifically for solar applications, so that they can accept a wide range of input voltage including low voltages. This particular controller may be fine, but it depends on the specs of the module. As soon as some current is drawn from the PV panel, it's voltage will drop. So I think under-voltage will be a bigger concern.

 

You can, but it's not ideal. It's hard to ensure the cells in parallel are very nearly identical. Manufacturers do it by using tight specifications and maybe even cell-matching procedures. Once the cells fall out of sameness, the controller can't protect them both at the same time. For a DIY project that is not terribly critical, you can probably live with this.
First let me point out that there are charge controllers designed specifically for solar applications, so that they can accept a wide range of input voltage including low voltages. This particular controller may be fine, but it depends on the specs of the module. As soon as some current is drawn from the PV panel, it's voltage will drop. So I think under-voltage will be a bigger concern.

Thanks for the help
I will use batteries from an old laptop battery so maybe they are identical and no problem will occur.
Alternatively I can use multiple charge modules and multiple batteries.

For the under voltage I can use the step-up (5 V) module but I don't know what will happen if more than 5 volts are applied to the Vin pin