battery maintainer?

If your generator is being ran 'regularly'- as you say it is, Maybe once a week ? You would not need a "battery maintainer".
These 'battery tenders' often produce as little as 1 amp and 'self regulate' their charge. The idea is to ensure the battery will not lose it's charge through natural losses and be unable to start your generator when required.

Does your battery have any caps? If so take them off and fill your battery with water. Do you have side or top terminals? If you do-not have them install washers on your terminals. Use battery jelly or terminal protectant usually terminal come in spray can. Make sure that your terminals are kept clean. This may help?

a maintainer only supplies a low level of current to cover the loads on that battery from systems that remain active, like the computer and radio.

Battery maintainers are just 2 amp trickle chargers that keep the battery charged for when you leave the vehicle sit for months in storage.

Battery trickle chargers/maintainers are intended for vehicles that seldom get use.

Like a snowblower or lawn mower.

Or car you only use once a month.

As time passes the cars battery drains. Either because of it's natural rate of discharge or the cars parasitic electrical draws(such as clock, alarm, cars ecu, all these need electricity to keep memory). So if putting the car on storage for the winter or, you are going on a long trip for months at a time. It's a good idea to get a battery maintainer to keep it top up.

You probably don't need a maintainer. Who said you needed one? If you generator and battery are in good condition and you start and drive the car regularly then you don't need one. A maintainer can be useful if your generator is weak or if you leave your car for long periods without starting it.

Battery tenders (trickle chargers) are used for cars that sit a long time between use. The can either be 110 volts or solar operated.

the generator is being used regularly due to cut off mains so why would i need battery maintainer for battery?

A, "battery tender," maintains a battery's charge by plugging into an outlet so you don't need to run a noisy, polluting generator.