1. USB charger.
2. Battery.
3. Boost converter.

I am looking to make something out of jelly bean parts if I need to put a circuit in place here. Like a transistor crowbar circuit, or something please.

 

If the battery specification recommends that the voltage is not to fall below a certain value – then the answer is yes.
Some rechargeable battery’s performance will be severely compromised if allowed to deep discharge.

It would be a relatively easy circuit design that disconnected the battery from the boost converter at a predetermined voltage.

 

Below is the LTspice simulation of a circuit that will cut off the output at its set voltage.
It uses a TLV431 (not TL431) low power voltage reference as a comparator controlling a P-MOSFET switch.
It switches when the Ref voltage equals 1.24V, as determined by the voltage divider consisting of U2 and R3.
Pot U2 can be adjusted to get the desired cutoff voltage for the particular battery you have (set for 3V in the simulation).
The P-MOSFET must be a logic-level device that can fully turn on at a Vgs of -3V.

 

I'm reading the specs on the battery and this is how it reads in the auction description:

3.7 Volts 5200 mAh 1S2P PCB Protected Battery Pack

MADE WITH HIGH QUALITY LG CELLS

Battery Pack Specification
Nominal Voltage 3.7V Nominal, 3.6V Working
Nominal Capacity 5200mAh, Minimum 5100mAh
Max. Charging current 2.6A
Max. Discharging current 5.2A
Dimensions (WxLxH) 20 mm x 40mm x 70.0 mm (approximate)
Weight 3.5 oz (100 grams)
Internal Impedance Internal Impedance: less or equal to 90 mohm (with PTC)
Cycle Performance 80% of initial capacity at 300 cycles
​

Then the questionable part is listed next. Do you read this as the battery pack as HAVEING the protection already, or as NEEDING it?
What do you think?

Protection Module Specifications

Over-charge protection voltage 4.325±0.025V
Over-discharge protection voltage 2.40V±0.100V
Over-current protection 2.2～3.4A
Maximal continuous Discharging current 2A
Maximal Current consumption 10uA
Short circuit protection Automatic Recovery
Protection circuitry resistance ≤50m​

As I read this a few times I feel like it may have built in protection, but ether way it appers as though 2.4V is the over discharge level for the batteries.

 

Below is the LTspice simulation of a circuit that will cut off the output at its set voltage.
It uses a TLV431 (not TL431) low power voltage reference as a comparator controlling a P-MOSFET switch.
It switches when the Ref voltage equals 1.24V, as determined by the voltage divider consisting of U2 and R3.
Pot U2 can be adjusted to get the desired cutoff voltage for the particular battery you have (set for 3V in the simulation).
The P-MOSFET must be a logic-level device that can fully turn on at a Vgs of -3V.

View attachment 167521

This is awesome I think I have all the components on hand.

 

As I read this a few times I feel like it may have built in protection, but ether way it appers as though 2.4V is the over discharge level for the batteries.

It does appear to have it built in, so you shouldn't need the circuit I posted.

 

It does appear to have it built in, so you shouldn't need the circuit I posted.

OK as I re-read there post a few times, I started to think that it had the module in it. But some times you need another set of eyes to assist you. On another note I think it would be in a good form to build YOUR circuit to "have in my pocket" in case I come across a case where there is not a module built in. So again thank you for that.