I've got a couple of the Maypole 4A and really impressed with them. Got one on the Mog and the ZX10 as I type. Much better than Optimates that I've previously used.

However, no use for a flat or very low battery. If the Battery voltage drops below 6V, it's 'Smart' thing assumes it's a 6V battery and will not charge it up to 12V.Throws a bit of a wobbler.

1972 4/4 4 seater, 1981 MGB GT
1984 Harley Davidson Electra Glide, 1990 Kawasaki ZX10