2002 sedona 3.5 battery/brake light 92000 miles.

sometimes battery &brake light comes on for a few seconds then goes out comes back on and goes out . It wont stay on. Sometimes the headlights pulsate . Went to start it , engine started to turn then click . Charger on the battery;; started today.Let it idle for 1 hr. went to move it ,it died and click no start. Jumped it ,let it run connected multi-meter to it,,, it’s showing 11 volts no more. .Put a spare battery in it and muli-meter reading 13 &14 volts with heater &lights the turned on.Still getting a dull battery/brake warning light but its still not steady. Cant check the alternator without removing the top rad.hose. to get to the big cable that goes to the back of the alternator. This Batt. Brake warning light bothers me . Any one have any Idea? Thank’s in advance Oh one more thing ,Its not been turning over as fast as it has before this all started.