Max, that ryobi ad is really grating on my nerves.

If you go to bunnings website you will see the battery lasts a super long 54 minutes...without load. Light load drops it to 45 minutes. No word on medium or heavy...
https://www.bunnings.com.au/ryobi-36v-460mm-hp-brushless-lawn-mower-kit_p0344062

Provided the old dinosaur victa deck isn't rusted, the old 450 briggs will also last a hell of a lot longer than that 36v excuse for a mower

Battery mowers have their place - its just not in any of our sheds haha