New gel batteries, charger puzzle

2003 E825 installed new gel batteries to replace the dead ones. Just got this car BTW. Charger came on with a high idle, red light, after a while idle came down on charger and red light blinks. I turned off the main switch and turn it back on and light goes to yellow, then green when charged. Anyone have any idea why it does this,? Why can I just plug it in and let it charge?


Red light at start of charge, then blinks at 80% charge, then goes to yellow, then to green