I have a 2005 XC70 which instantly drains the battery. I've just put in a fully charged battery, it made a brief ticking noise when I attached the negative lead and it instantly drained the battery. I mean in a literal second, drained a full battery!
No previous warning signals/messages/lights. I suspect a massive short somewhere but it's happened sometime between me parking it a couple of weeks ago and yesterday.

 

One thing is for sure: Huge unfused short circuits, with huge conductor paths to and from the problem, are always going to be easy to find. So that's lucky. If you really did discharge a good battery in under a minute, the heat (and possibly fire and smoke) would reveal the whole path of the circuit.


There are a couple of other possibilities I want to just mention. The first one is hard to diagnose on the internet. That is, that every car I have ever owned would lose power due to corrosion on the battery terminals. The battery would still be okay but the car does not have any power.


The second possibility is that the battery was no good and/or dead.

 

That's what I thought as well! There would be sparks, smoke, fire and all kinds of Hell going on, but there was absolutely nothing but a bit of clicking from the left of the battery where the rear fusebox is housed. I checked that, and there's no damage, not even a blown fuse.
There was no smell of melting plastic or fried electrics, I mean there is just nothing. Not a thing to point in any direction. The battery is almost brand new, all the cables and wires look well maintained and serviced, there's hardly any dust on them even, let alone rust. The battery was fully charged according to the charger at least and it showed no battery charge after the incident, so I take that to suggest the battery is ok.