The solenoid is just a coil with a sliding spool, when you hit the solenoid with the hammer you dislodge the interface between the spool and the coil, so unless the power is left on, which means you have a 'held start function' on the ign switch I cant see it related to be honest. Significant voltage drop though, 1 V. I killed a battery crossing the Simpson with a Finch Fridge, brand new, but the Finch has no thermostat on 12V, I arrived back in melb with a new Century wet cell at 2V - battery rooted, no warranty - would not think its a catastrophic all cell failure - look at the aux items connected I reckon.