As per the questions about the Univolt system, and whether they automatically charge the battery, and what year they started, I can quote from my 1975 owners manual. Obviously, as has been pointed out here by folks much more knowledgeable than I, the univolt system is by now ancient technology. But hopefully this helps those who may not have access to an older user manual. I was fortunate to get one with the '75 Tradewind I recently purchased. To quote the manual exactly...
"When your Airstream is hooked up to 120 volt A.C. the Univolt System automatically charges the trailer battery and, if it is hooked up, your automobile battery as well. The speed and degree of charge depends on how much power is used for lights and appliances, as only the surplus goes to charging the battery.......Whenever possible, use the automatic built-in charger of the Univolt System for charging. The charging circuit automatically controls the current, reducing it as the battery increases in charge."
I do hope this helps.
Robert
