As batteries get old they degrade in their ability to hold a charge. Wouldn't compressed-air hybrids be better

Compressed air is inherently dangerous. If a battery was involved in a crash, it would just leak liquids. If a compressed air vessel was involved in a crash, it has far more potential to add destructive energy to the situation. If the compressed gas is hydrogen, then the situation gets even worse, because when it mixes with oxygen in the air, it becomes explosive.