Update, it's now 3 hours and 20 minutes and the consumption has dropped to 350 watts. I assume it's now in a constant voltage phase of the charge. It looks like if you were on a trip you'd only let it charge to this point before heading off on the next leg.
Update of update, there's actually a light on the bike that indicates the bulk phase is finished and the absorbtion phase is running. Its symbol is a battery that's nearly full (makes sense I suppose). When the amber light by that symbol is lit it's in absorbtion. So if you can see 3 amber lights it's time to roll again on the next leg of the journey.