What a shock!

I took a voltage reading on the old battery with my multimeter and it was registering 12.43 volts so it isn't totally dead. I bought a smart charger from Lidl and I've got it on charge. After I'd removed the battery, I found out that it is a calcium type so there's a chance that it could be saved. I've also fitted my earth lead so there should be a decent earth once I come to try starting the car again.