Bongo Fury

Halfway home driving from work (weekly Bongo run), my Charge Warning light comes on +stays.
At home I measured 12.2V while running, not 14V-ish. Oh dear has my Alternator failed?
New one ordered, but my preferred specialist to fit it is 90 miles, 2 hours away (Steve @Outback Autos).

??? Will my Battery get me there, assuming this Alternator is dead/has ceased to be ??? (95Ah "heavy duty" Varta, less than a year old).

??? How much current does a 2.5 V6 petrol drain when running, with "minimum" electrics ???
I would drive in daylight, without heater, aircon ?radio/CD. But Engine etc, brake lights, wipers ..
I could "fast charge" main battery for 10mins or so (once it has started Bongo), and will pack my spare battery (fully-charged with spanner).

Or am I an idiot asking for a breakdown, ie should let a local non-specialist work on it?
Advice appreciated

I would have thought you'd get away with that, especially with the back up of a second battery.

Having said that fitting an alternator is pretty straight forward so I'd consider DiY or local garage, if just to save money on fuel.

I got mine done 15 miles away by a non Bongo specialist for £25. Your petrol costs will be more than that, as Bob says. I reckon you'll make the 90 mile journey if you try it.