There may have been different Univolt versions, some with battery
charging and some without or that feature has broken.
In my opinion as an electrical engineer, I'd go with some
charger/inverter like from Statpower and leave that original AC/DC
switch in the DC position. Hook the charger/inverter between the AC and
the battery lines and remove the Univolt. Put it on a museum shelf if
there's one strong enough to hold it. When AC is supplied the
charger/inverter will charge the battery and without AC it will supply
AC on demand. It can be connected in parallel with other battery
charging sources such as the tow vehicle charging line. It won't be
cheap (e.g. $100) but will depend on the inverter capability. Some such
units for house sized solar systems run as much as $2400, but you don't
need that much power in the small Airstream. You can run everything
needed from 12 volts except the VCR (as far as I've noticed) so don't
need a lot of AC power. The battery doesn't have the power storage to
run an air conditioner.
OR there's some very good battery chargers that do more than just supply
some DC from Statpower. They condition the battery, charge it and pamper
it for greater battery life. Then choose separate inverters for the
necessary AC loads that match the required load. Efficiency will be
greater that way. A 50 watt load on a 1000 watt inverter isn't nearly as
efficient as that load on a 50 watt inverter. But the individual
inverters aren't as neat an installation and require individual
attention when changing the AC devices to AC power... But with a good
charger, the losses with the intermediate DC link are not expensive.
There are other sources, but the Statpower line seems very available and
their web page (www.statpower.com) has a lot of technical information.
Gerald J.
