Battery lawn mowers

I have the einhell power x-change one and it's very good. If the grass is long, I just cut at a longer length and then go across again at a shorter level to stop it getting blocked.

I have no experience with any of the current new models but tried a few different 18v mowers around £250 years ago and they all stopped spinning if the grass was more than a few inches and if they could just about cut it the battery would die really fast.
Did my research and purchased the erbaurer 36v 46cm metal deck mower and its fantastic been using it 2 years now, cuts through pretty long grass upto around 6 inches no problem and runs at a lower speed on short grass to save battery power, when it detects long grass ( im guessing by resistance) it speeds up the motor and ploughs through it.
Build quality is really good with the metal deck and wheels are good big size.
Its over your budget at 400 but its really good and can cut a huge garden on a single charge (edited)

i have a ryobi one

its pretty poor tbh, but i have a small piece of grass, so not that much of an issue

I had a Titan (Screwfix) one a while back before I replaced the lawn. Was very impressed - done a bit of research as the reviews in general were poor on most brands - battery life poor, can't deal with longer grass etc etc.

This looked a solid build and it turned out as expected. Battery life was fantastic (small lawn - 250sq feet) - 5-6 cuts before it needed charged. Coped with the longer first cut of the year (and it was wet grass) with ease - highly recommend it. They have a few on sale - all the same machine, just different widths

Makita one, alot of electric mowers come with a unsharpened blades also well worth removing and sharpening before using.

Aldi have one, looks small and needs a battery, but a 3 year guarantee. Might be worth a punt?
aldi.co.uk/fer…400