Low Volt DIY UPS Project #1 Stream: The basics. Charging lead-acid batteries. CC and CV

Low Volt DIY UPS Project Stream #1. Read the full description.
In this video we discuss basics: the whole idea, characteristics of lead-acid batteries, how to charge them properly, controlling voltage and current. Also we try to use a XL4015-based board to charge a battery.
This is video of my Twitch stream on March, 5th when I started the low volt DIY UPS project. It's not edited, so there is A LOT of water.
Since I have a very little knowledge of electronics, this whole project is only possible for me because I actully can buy all the major modules of the future UPS on AliExpress for cheap, I don't need to come up with anything myself. The rest will be mostly just connecting them to each other and figuring out the right modes of operation. Anyway, it's going to be a journey, both for me and for the viewers.
Why do I need an low voltage UPS? I don't know, since I have some nice sealed lead-acid UPS-grade batteries around - the most expensive part, - it just felt like a good idea.
How am I going to use it? As a power source for one of my routers (19 volts), for my Wi-Fi access point (12 volts), probably as USB charger (5 volts) and for some emergency LED lights. No adjustable output, just a bunch of fixed voltages.
This was streamed live on my Twitch channel: / callmerive​ . I'm mainly a DayZ streamer, but sometimes I play other games (GeoGuessr, Star Citizen, Minecraft), build PCs live or try to solder things together (real basics, for example: 10-meter USB cable, fixing a monitor's PSU etc).
Follow me at Twitter @callmerive: / callmerive​
Links:
XL4015 board (actually, don't recommend for more than 12 volts and 2 amps, I'm going to try 300 watt version of XL4016 instead).
www.aliexpress...