The battery guy asked if the voltage regulator was OK, since over-voltage will do this sort of damage (acid everywhere, very low voltage, battery not charging). I shrugged and said "presume so. It's fairly new". It was also only a year or two old (probably less), but I got the old multimeter out and checked. Seems the guy just saved me another $160 (I stopped measuring when it got to 16.5V and turned the engine off). Buy one here and you will pay $125 (pentastar) to about $200. In America, you'll get a brand new one for about $2.95 but only if you live there. Those who sell to us charge about twice this. I landed one for a bit under $12, but it took two weeks. Now the Valiant is up and about again, and I have to wonder why the massive price difference. It's not the usual twice or three times as much like we're used to. We're charged over forty times what the Americans pay. No wonder the Internet is so popular. Unfortunately I missed the Ballarat swap meet because of the time taken (it arrived the day after).
When I was investigating the regulator, I found out that the Valiant's Ammeter is a major point of failure. No other car manufacturer threw 100% of generated current through the firewall (twice). This is bad, because as the car ages and the wires start to corrode, resistance increases. The physical effect of this is that the wire gets hotter. Frequently, the connectors melt (they are plastic) and everything short-circuits. It scared the bejesus out of me and I'll make conversion to a volt meter and re-routing of the alternator output. Here are some relevant references:
Replace your alternator and regulator with electronic variety
Explanation, and instructions on re-routing the wiring and replacing the ammeter
