YES.
As long as you connect it directly to the battery..
Cheers guys that will do me.
I was just worried it might screw the canbus but it would appear not. Time to get the spanners out.

so over winter is it ok just to use a 12 volt 4 amp battery charger, connected by crocodile clips straight to the battery, once a month or so, for a few hours, just to keep the battery topped up,
rather than buy all the expensive fancy canbus optimate stuff
You could connect the bike batter to a big (car) battery and charge them as a pair.

so over winter is it ok just to use a 12 volt 4 amp battery charger, connected by crocodile clips straight to the battery, once a month or so, for a few hours, just to keep the battery topped up,
rather than buy all the expensive fancy canbus optimate stuff
You really want something that charges at 10% of the battery capacity or less, so 1.2 amp/hours.
Charging at 4a/h risks boiling the battery up. You could connect the bike batter to a big (car) battery and charge them as a pair.
A normal Optimate or similar is a better option though. LIDL sometimes do one for £15.
There appears to be some misunderstanding of the concepts involved here. Amp-hours (not Amp/hours) is a measure of a battery's capacity, *not* the rate at which it can be charged (or discharged). To talk of "charging at 4 Amps/hour" is meaningless.
And you should *not* connect dissimilar batteries "as a pair" as a means of limiting charging current. If the other battery is already fully charged, the charging current through the partially discharged one may well be even more than the charger's rated output...
