Sounds like a problem similar to mine a while back, and the regulator was to blame. Contacts were intermittently switching.
Kept having to top the battery fluid levels up, and at one point the battery blew up on a long journey. Remaining acid sprayed up on to my jeans.
At this point the Johnny Cash song "Ring of Fire" sprang to mind.
I've now fitted a solid state regulator and a voltmeter between the speedo and tacho "just in case".