sleep in Bash if/else sleep vs <condition> && sleep clamining cpu

I wrote a script to check on the battery and if it is below 5% notify the user. The script is put to sleep for 1 minute after every check. If I write the script in the following way, the cpu workload will rise to great extend:

#!/bin/sh

while true; do
  [[
    $(
      upower -i /org/freedesktop/UPower/devices/battery_BAT0 |
      grep percentage |
      grep -Poe  "\d*"
    ) -lt 5
  ]] &&
  notify-send "Battery below 5%" &&
  sleep 60
done

Do you know why the cpu went up? You can see in the image, that a lot of cpu resources are claimed. They will not be cleared. If I write the script in a more conventional way, with simple if/else blocks, everything works as expected and the cpu will only go up for a short time in the beginning and after the sleep period is over:

while true; do
  if [[ 
      $(
        upower -i /org/freedesktop/UPower/devices/battery_BAT0 |
        grep percentage |
        grep -Poe  "\d*"
      ) -lt 5
     ]]; then
    notify-send "Battery below 5%"
  else
    sleep 60
  fi
done

Do you know why this behaviour is happening?