Can the internal sensors SRTPP400 be used with the app?

Sorry, the internal sensors are not Bluetooth and cannot be used with APP

I have the SRTP300 kit with the sensor caps and love it, it has already prevented me from being stranded! I want to upgrade to the internal stems / sensors but need to know if they come in black. Most bike wheels are black so I need something that matches. Thanks, Brian

Thank you for choosing SYKIK. Our SRTP400 is acktually not silver but light blueish crome, looks ok with black or silver.

What size stem do these fit??

Fits rims with 8mm stem holes

Do you have internal sensors for commercial vehicle tires??

Yes, we do carry internal sensors as well. We can offer them with any of our SRTP901 units. Just let me know how many internal sensors and how many external you like to have, we casn make the set for you. You can see the internal sensor here:
https://sykik.com/products/internal-sensor-for-tuck-rvs?_pos=1&_sid=8092710a9&_ss=r

Do valve stems come in 45deg's also

Correct, comes with 90 degree stims as in the picture

Is the internal battery of the 90 degree sensor replaceable and what is the battery number?

The batteries are not replaceable, since the sensors are sealed. Life of a sensor battery depends on how often you ride, and how long. Avarage rider should expect about 3 years of battery life.