A standby generator and a home battery both keep the lights on, but they suit different outage profiles and different budgets.
How long are your outages?
Batteries are excellent for hours and poor for days. A generator is the opposite: noisier and needing fuel, but it will run for as long as you can feed it.
What do you actually need to run?
Furnace, fridge and a few circuits is a very different job from the whole house including air conditioning. We size the transfer switch around that answer, not the other way round.