I have something like the aldi offering which gives a trickle charge, great for keeping the MGF ready. However to revitalise a flat battery you need a reconditioning charger -
http://www.ringautomotive.co.uk/cats...cat1=7&cat2=31 gives more info, I have the 8 amp model which has saved several dead batteries, if you get up to me you are welcome to borrow it.