Zero experience with EV relays, but .5kWh per 24hrs (21W) sounds like quite a lot. Do they get hot?
Again, not sure if it's recommended/required for that particular relay, but there are very simple circuits to significantly reduce operating power requirements of DC relays:
Panasonic Products for Energy Management. Recommended products for specific applications. (Photovoltaic Power Generation System/Power Storage System/Quick Charger Stations/Smart Meters/Rapid Shutdown System)
www3.panasonic.biz
Section "1. Example of CR circuit method", requires just 3 very basic parts.
Essentially, it initially allows full power to get the switch moving. And then reduces the current once the relay has settled in the closed position.