Battery Dead

Back from a great month-long holiday (Touring the West Coast of the USA, Cayman Islands, Bahamas & then Washington DC) and settled back in.   
 
So got to the car and she was dead.  And I mean totally dead, 0V showing on the voltmeter and nothing showing on a meter across the terminals of the battery. and it would not register on a charger.   I knew the battery was on it's way out, but I have never seen one fail that comprehensively.   Luckily (or forward planning ?) I had bought a new battery some weeks ago so out came the old one and in went the new one.   All the lights came on and she started up instantly, even though she had been sat for a month. 



I suspect I broke the battery myself by leaving it on a trickle charger when not in use over the last few months (not while we were away though as I wanted to see how the battery was looking).   It was supposed to be a 'smart' charger, but I only ever saw it pushing it out 14V so I suspect it was continually overcharging the battery.  It was a cheap one from Lidl, so I think I will just use it as a normal charger now and just charge the battery when it needs it.