I have a '95 E320. Today after about a 15 minute drive in 100 degree temp, when I got home and turned off the car I could hear a boiling sound. When I checked under the hood I found the battery was boiling like crazy. What could be the cause of this and how big a concern is it?

Thank you for any help on this.

 

how old is your battery?

two reaons: battery and alternator.

if the plates inside the battery is bad, it will boil.

if the rectifier/diodes or voltage regulator inside the alternator is bad, it will overcharge.

 

Both the alternator and battery were replaced two years ago. Is the best way to test this just by getting a battery load check and\or electrical test?

 

the battery is old.

if you disconnect the battery with engine running... the engine will stop? check how many volts on that cable terminals.

check the battery voltage and current using load test.