The Baofeng GT-5TP appears to be a UV-82 derivative… there are many such derivatives. The battery supplied is labelled BL-8 and rated at 2000mAh. It seems that Baofeng makes two incompatible batteries labelled BL-8, a slightly different (but incompatible) BL-8 battery is used on the UV-82.
Of course it is supplied with a Chinese power supply that does not comply with Australian Standards, and is illegal to sell in Australia, even second hand by an end user.
It seems common that Baofeng portables use a charger cradle that is powered from nominally 10VDC. The question arises as to the maximum input voltage.
The PCB silkscreen identifies a SC6038 charger chip, and the datasheet for that chip specifies a maximum input voltage of 12V. This is hardly convenient for charging from an automotive system where voltage may well reach 17V under some charging conditions.
Disassembling my one revealed a different chip fitted, a HXN-WS for which I was unable to find a datasheet. In the absence of information to the contrary, assume it is equivalent.
So, it is prudent to label the charger “12.0V Maximum” to avoid damage should someone try to power the thing from an automotive system.
Further, in sourcing a safe standards compliant power supply, it needs to be no more than 12.0V, preferable closer to 10.0V.
To use this thing in a car, one needs an external DC-DC converter that accepts 10-18V input and produces 10V @ 0.5A.
I have seen a mod to reduce charge current from 1A to 0.5A, but I wonder if it is needed, mine has never charged more than 0.45A.
I modified the charger cradle to add a short external cable connected directly to the battery contacts and terminated in an Anderson Power Pole connector for connection to my Westmountain CBA for battery testing. Of course the cable needs labelling to prevent it being used for power input. (This battery can be discharged from the external terminals, keep in mind that shorting those terminals could have serious outcomes.)
The radio is 5 years old at the time of writing, and the proprietary batteries are unobtainable. That is not unusual for Chinese portables, common for Baofeng.
A discharge test indicates 60% capacity at 0.5C. In my experience, one is lucky to get that out of a new Chinese battery. The curve suggests that the battery has internal over-discharge protection.