I would have thought this would be fine - so long as you use a
'trickle' charger and don't try to put mega amps through it.
Obviously check that the socket is live with the ignition off....
I use a Ctek charger on mine (Aero8), but have a dedicated line/socket for the purpose.
On the Trads,many folk fit the Ctek trailing socket through the rear bulkhead and behind the seats.
Check out DaveW's post on this (or buy his book...

)
James