Since batteries are good at producing heat during normal use (both discharge and charging) I’m personally wary of relying on hot glue.
I’m still trying to figure out exactly where I want connectors on my systems. I recommend some sort of disconnect between the battery and the PCB.
I built a 3S LiFePo pack for accessories on my bicycle, BMS, external charge connector. The BMS is attached to a blank PCB. When I want to remove it to add a 5V and 12V DC-DC converter, the battery is currently soldered directly to the BMS and isn’t separable from the PCB, so to work on it, I must work with the whole system /live/ which I am not fond of. If I misplace my soldering iron, I can short out the P-/+ terminals, or drop a screwdriver across the BMS and short out the pack directly. Adding a disconnect is probably first on my list of things to do.
I own a lot of “cell phone” battery packs. I think the biggest is “25 AHr”. I’ve wired 2 packs in series to make 10V for my bicycle headlights, but the USB-A connectors have worn out with vibration. I can reliably pull 2A out of the bigger packs. Note that in some of the packs I’ve broken the USB-A jacks off their PCBs, but resoldered them. I have not tried paralleling two USB-A connectors for higher draws (i.e. 3A). Newer USB-C packs can output 9, 12 (optional!?), 15, up to an eye-watering 20V @ 5A (100W). However, to use those modes, you need a “usb-c trigger” module to negotiate the output for you. I have not bought any of these newer packs yet; I’ve made the 25AHr pack my EDC (kinda heavy, but heavy gaming use), but I can power my phone for several days; I can forget a day or two of recharging and not sweat it.
The nice thing is that you can short these packs out and they’ll simply shut down. Caveat: you need to plug it into a charger to wake it back up. If you have multiple packs, great!
If you need 10V, and are using more than one device, make sure you label them as 0-5V and 5-10V, and pack A gets both 0-5V connectors (as both grounds are shorted together), and pack B gets both 5-10V connectors. Not doing this will effectively short out the pack outputs (i.e. short its ground to its 5V output pin).
Headache: Pushing a button to wake up is annoying. Sometimes this style of unit will shut off with too small of a power draw (like a GoPro that’s reached 100% state of charge, requiring you to wake the pack back up before you turn the device on. It’s nearly impossible to tell whether a pack is push-to-wake or always-on. It’s also nearly impossible to tell whether a pack is “charge-through” i.e. the output does not shut off when you plug in a charger. A always-on charge-through pack can be repurposed with zero work into a “UPS” for a 5V device such as a Raspberry Pi.