Hello - I have a 280c collar and transmitter. Which size batteries do I need?

For transmitter - Item #: PSU-BP37T https://www.dogtrainerstore.com/products/dobpiqtrba?variant=58843648907
For collar - Item #: PSU-BP37W

https://www.dogtrainerstore.com/products/dobprebafor2?variant=58843499915

Can I replace battery in iQ Plus 112524

Yes you can. For collar/receiver - Item #: PSU-BP37F https://www.dogtrainerstore.com/products/dogtra-bp-37f-battery-for-iq-efence-ef-3000?variant=58843648779

For Transmitter/remote - Item #: PSU-BP37T

https://www.dogtrainerstore.com/products/dogtra-bp37t-iq-transmitter-battery?variant=58843648907

Which battery fits the 280 NCP receiver ?

Dogtra BP12RT Replacement Battery , Item #: TSC-BP12RT  would fit with 280NCP receiver.

Hi, can you please tell me if the batterie for the collar receiver ARC can be replace with the batterie 280NCP?

No you cannot replace with 280NCP battery.