You want hardline, like Heliax (Comscope/Andrews) or whatever RFS calls it. At 50', you are looking for 1/2" or 7/8", unless you can find a deal for larger somewhere.
As mentioned, testing of an HT antenna is nearly impossible to get completely accurate results. It should also be noted that sometimes a "better" antenna will cause the radio to perform worse due to RF saturation. That being said, for the APX, the Motorola antenna will work the best for that radio.
Other than shortcuts, the keyboard is only useful for DTMF tones, which could be used to control a repeater's features, such as changing the input tone, or disabling the repeater during a malfunction. It's not a huge selling point for many radios.
It's in the rules.
Fixed station. A station at a fixed location that directly communicates with other fixed stations only.
Base station. A station at a fixed location that communicates directly with mobile stations and other base stations.
47 CFR 95.303
An example of a fixed station would be an RF link between 2 repeaters. They only talk with each other, at fixed locations.
Anything commercial from Harris/Motorola/Kenwood
TK-3140 has Part 95 approval and can do multiple zones up to 250 total channels.
You likely won't find anything in the cheaper chinese radio market.
4 isn't really that many if you have difficult terrain to overcome. Yes, it's an investment, but if it's useful to you, who cares. Now, having 4 tower leases, or even have someone willing to lease you tower space, that's the impressive part, considering crown castle won't even return a phone call.
Yea, all my LiFePO4 batteries are bioenno, and I bought their charger with the battery. They do stop charging (LED goes green from red) when the battery is full.
An external antenna would probably remedy your solution over an HT in the car. Doesn't matter if it's the same frequency, other electronics tend to not like transmitting anything near them. Computer screens, computer speakers, etc. all complain when even 2W of VHF, UHF or 6meters is transmitted within a few feet.
Not when the radios themselves are 20+ years old, and were first programmed with a true serial port.
I can't remember if the TK-880 needed booted up in a programming mode or not. I guess check the manual to see? That may only be for firmware updates though.
You won't find them new anymore. TK-3140 was a great Kenwood that has Part 95 certification. They used to be $70-110 used, I still have a handful of them, used the KNB-55 battery, which is also used on the NX-3000 radios.
These guys check the radios out before selling them, for $150 its fits your budget https://used-radios.com/kenwood-tk-3140-uhf-450-490mhz-250-ch-4w-portable-radio/?srsltid=AfmBOor3hXfzNg6frpl6zsTfAzixQGKZJjih1N4fJGGRJn8_YKKdad4w