Clever people, please, your opinion is needed. I am fed up with the constant power outages so need and online ups to keep the computers routers switches and firewall running so need a 2000VA supply - we intend to supplement this with a deep cycle battery and an inverter to extend the UPS battery life. We found this on MS electronics CyberPower OLS2000EA 2000VA Online UPS LCD but the battery is not replaceable anybody got any suggestions? 

I would opt for PV-ready solutions, like EcoFlow Stream

Thank you but we need an online system with no switching.

It does not require any switching - thats the beauty of this system, look for the description

У базовых ecoflow были очень плохие болячки типа отключения питания по достижению макс мощности, просто отключение питания в рандомные моменты и во время апдейта системы. Надеюсь здесь починили