Typically, EVs have main drive batteries that are around 400V. This would be enough to toast an old-tech car’s electrical system.
All EVs are equipped with a secondary 12V system that powers the car electronics. The main battery charges this battery. You can remove the nosecone from a Model S to attach the 12V system. This could be used to jump-start an older model car. In the early days of Model Ss, the car was too protective of the 12V system and would cut the link between the main battery and the 12V batteries. This would result in the 12V battery draining overnight.
The main drive battery keeps the 12V battery charged, so it isn’t necessary to be strong enough to start a starter motor. It is, therefore, a small motorcycle battery in the Model S. This can be damaged by jumping start a combustion engine.