Originally Posted by 73shark
I seem to have forgotten the purpose of the Aux battery under the hood in the later models. Since it can't be used to start, what is it's purpose? Can it be charged by anything besides the alternator?
It's optional Sprinter equipment, not installed by Airstream. It's normally used on commercial Sprinters such as ambulances and television news trucks as a "house" battery. As such, when Airstream installs house batteries at the rear, the auxiliary battery under the hood is redundant.
hook up stuff like the awning and sliding step to the auxiliary battery so they don't draw off the starting battery, but they don't. So the auxiliary battery is pretty much dead weight, unless you install an aftermarket alarm system or something and hook it up to the auxiliary battery.
And because of the way it's wired through a relay, the auxiliary battery IS only charged by the alternator.
I suppose it's possible to remove the relay in order to provide a permanent connection between the starting battery and the auxiliary battery, thus giving you two starting batteries and doubling your cold cranking amps. Which could be handy in cold climates if you don't have indoor storage.