I have the same V70, but I had this same thing happen to me with my OK I'll say it Honda Civic. Sorry guys but my wife bought it. Anyways I was parked and the car battery was dead as a door nail. No life whatsoever. So luckily I was near a Lowe's and bought a portable charger and wasted 2 hours of my life waiting for it to charge at Lowe's. Came back to the car and I decided to try ignition one more time before charging the battery. The car started right up. The battery definitely needed replacing, but letting a dead battery sit for a while it can build a slow charge to start the engine. Hope this helps.