I've not weighed mine on scales but I reckon 5-6kg in one pannier - a lot of which is 2kg of lock. The rest are my clothes, washing stuff and other bits and pieces like wallet and phone.
Maybe it's because I'm relatively new to panniers but it makes the bike really heavy - enough that I got a pinch puncture riding in to work last week - a rough bit of tarmac to be sure but on an unladen bike I reckon I would have just ridden over it...
I can't get a lighter lock which is still compliant with my insurance (it's a Kryptonite New York Fagheddaboutit D-lock) so I think I'm just going to have to get used to it but does 6kg seem heavy for a single pannier?
Nah, not at all.
Maybe bungee the lock to the top of the rack rather than the bag and it'll help balance things a bit more.
Upto 25kg between the pair btw.
Yes, bikes feel heavier with panniers, but 5-6kg isn't much really. I'll regularly have double that each side when shopping on the town bike. It is worth balancing each side until you get more used to it. Could you put the heavy lock on a frame bracket or on top of the rack?
Leave the lock wherever you use it most and pump the tyres up harder to avoid punctures.. Next.