Shown below is a list of optional features that you may encounter in regards to generators.
Low Oil cutout
A low oil warning is important, but only if there is someone nearby to hear it - it is far safer to have a cutout which stops the generator in case of low oil.
Not really optional, but the more sophisticated ones will protect against over-temperature as well as over-current, over-voltage or under-voltage (that can damage some appliances)
It’s easier and safer than having to open the fuel cap!
Earth leakage protection
Bigger generators may have these built-in, but they can be easily added.
You can get by without voltage, current or frequency meters, but with them it’s easier to check if your system and appliances are healthy or if you are close to overloading your generator.
Battery Charging output
Whether you buy the cheapest two-stroke or the most expensive Japanese Inverter generator, the built-in charger is still totally unregulated and you could cook
your batteries in a few hours. Consider this an emergency option only, unless you like living dangerously.
Nearly all Inverter Generators have this built-in to reduce fuel use, noise and wear.
Paralleling two Inverter Generators
You can directly wire the DC from two batteries together, but you can’t do this with AC because the voltage changes from plus 335 volts to minus 335 fifty times a second. If you connect them at the wrong time there’ll be a big bang ! The outputs from two AC generators can only be connected together to power bigger appliances if the generators are synchronized so that positive peaks occur at the same time. This requires a special cable and connections, so if you need this capability, check before buying your Generators.