New battery, car wont start. lights everything all strong. Jump cables dont work on 2000 Mercedes-Benz E320

yesterday, car sluggish turning over. car sat for a while, sluggish starting again. 1 hr later, appeared as if battery was stone cold dead but lights and everything at full strength and never got malfunction light telling me the battery was bad or going bad. I left the lights on for a while and they never started to dim. I tried both keys but the car doesnt even try to crank or make a noise, dont think its battery or alternator. Any suggestions, I thank you.

Asked by for the 2000 Mercedes-Benz E320
Could be voltage regulator or bad starter too. When starters start to go, they pull a lot more power than normal and can make it look like the bettery is dead. Best way to check it out is to have an electrical system test run on it. Your local shop can do that, or AAA has a portable electrical system tester they can use if you have AAA membership.