Electric mower batteries

The first set of batteries we had in the mower (from new) lasted around 9 years.
When they no longer had the power reserves to mow both the front and back lawn, we replaced them.
(So in other words, they died slowly).
The replacements lasted 18 months and died ‘overnight’.

I have just ordered another set.
A different brand, but frankly, I don’t hold out much hope.
Dad and I have been talking batteries via email for a few weeks now so the timing of the mower batteries dieing was pretty crazy.
He has been having similar problems with electric scooter batteries…. Very similar load to mowing I suspect…. they (the new batteries) are just not lasting.
Its like they are printing any old amp hour rating on the battery.

80 bucks buys a lot of petrol, but both Freddy and I love the quiet power and easy start of the electric.
Neither of us want to go to a cord electric, so other than pony up and spend the money, I am not sure what to do.