200 pounds of clock in a seat, and 300 pounds of battery with a removed seat. That's on par with simply having two people sit in the middle row.
With 3 expensive clocks, 3 priceless kids, not to mention hot coffee in hand, I accelerated and decelerated modestly. The drive from Bellevue to Paradise Lodge up on Mt Rainier is mostly rural and then follows a long slow winding mountain road to 5000 ft elevation.
Besides, it’s not just the pounds that matter. Would you rather be hit by 200 pounds of hardness/sharpness/person bouncing to-and-fro or not be hit at all during a car crash cause that 200 pounds, whether object or person, was secured?