Been driving our Rav4 PHEV for 2 years soon. My wife drains the battery once a day on her way to work. We still get 65+ km (40 miles) in winter and over 80km (50 miles) in summer, driving mostly in the city.
All your buoyancy comes from non rigid devices (vest, suit). As you go deeper those devices compress and you lose buoyancy causing a feedback loop. Compounded with loss of vertical references, you can quickly sink to the depth where the air you breathe will become toxic. At that point you don’t have the mental capacity to save yourself.
