Fisrstly, it's not possible to spawn in empty carbatteries. using "0" as minimum value will result in fully charged carbatteries spawning in.

However I'm using

<quantmin>1</quantmin>
<quantmax>8</quantmax>

for the carbatteries and they spawn as intended; very low charged.

When using a very low charged carbattery, starting the engine of any vehicle, the carbattery will instantly die and the engine will obviously turn off. The carbattery will show an empty status bar. However after a few attempts starting the engine anyway, the engine will magically turn on and will slowly recharge the carbattery again. I guess this behaviour is not intended.