Battery boils over - Is this an overcharge or alternator issue?

[XS29L9B]

About a year ago I had an issue where the battery was dry. Didn't think much of it, just replaced the battery and moved on...

Drove the 87 TR the other week and when I lifted the hood, found the battery to be wet near the vents. It was water from inside.

Another TR guy suggested overcharged battery might do this, but nothing concrete. If you have tips or ideas on what to meter and where, please let me know so I can chase down what's happening. Thanks.

 

[Chuck Leeper]

1st test: Check the output voltage at the alt hot stud, engine idling.
Wash the area around the battery. Those fumes will eat the paint in short order.

 

[XS29L9B]

Will the alternator output change over the course of the car warming up?

I do plan on washing the area tomorrow after testing, as you suggest. Thanks.