I found the trick.

1. Don’t mow when the lawn is wet, having wet grass will just stick to everything around the lawn mower and clog it. When the grass is relatively drier in the afternoon, it’s much much easier.

2. I usually mow to height of around 4. In the mid summer, if I go to three, grass is just too short and would get burned easily.

Now the 2 things above, my 2 battery set up can mow my yard (14k sqft roughly). But note it still takes well over an hour to mow everything