Electronic – PMIC with Li-ion charger, stable output and USB OTG

Your design will trip the PTC polyfuse in your USB port when the load demands 500mA and the battery demands anything significant. Since USB2 only supports 500mA max. USB3 supports 900mA.

It is not clear to me how your device load is switched on/off so you need a smart load sense switch to U1 CHRG using a comparator.

But it is clear to me this approach will not work. YOu want a trickle charge when your device is off, so the USB can power the unit and the external Li-Po can get a trickle charge, If I understand you are saying and then when the USB is off but your "load is still on" it can run off the Li-po as long as it is charged.

What you could do is .. add a small shunt resistor between USB (Vbus) and LOAD (VSWITCH) with a comparator to disable U1 CHRG when there is current being used. .

This means I should be able to use my existing USB car charger that outputs 5V/2A and my existing USB charging hub at home, right?

No. The VX-8R series radios require 11-14 V DC (Negative Ground, EXT DC jack) input to charge ("Operating with Charging" pg 166 of the Operating Manual). Take note of the PA-48B charger:

Can I literally just chop off the integrated cord that runs out of the car charger and solder a full-size USB connector to the end and call it good?

No. Not only does your device not support 5V charging, but it is also not a qualified USB device and can neither negotiate power delivery nor respond to different chargers.

If I connect this new USB connector to a battery (such as one used to recharge a dying cell phone) is there any possible problem with this increased output wattage connected to a battery instead of to an actual continuous DC power source?

Since your device **cannot* be charged by 5V from USB, a cheap lithium battery pack for USB phone charging is not appropriate.

However, for continued operation at high power, you could use an external 12V lead-acid battery (car, motorcycle, marine) connected with the correct polarity to a barrel jack to supply external power such that your radio will operate in high-power mode. When using such a battery, be sure to use fuses to reduce the possible damage from the high-current capability of a lead-acid battery.