I'd definitely check the levels and top up if necessary.
The CTeK has managed to achieve step 4, absorption. It's attained over 80% capacity.
#11: I'll be honest I'm not overly keen to open it up.
Can you say why? After all, checking electrolyte levels should be part of regular maintenance, especially if the battery spends long periods on a conditioning charger.
Why? The internals being rather unpleasant.
In 26 years of driving, I've never opened a car battery, and might have replaced maybe 1 or 2 batteries in total.
The Banner isn't a maintenance-free type. As John says, checking the electrolyte level needs to be part of the regular maintenance routine. If it spends a long time on a conditioning charger it WILL electrolyse water off and the levels will drop. Mine needs toping up every spring when it's had extended periods on the conditioner over winter. The internals really aren't that nasty. You just need to flip the little caps open with a coin or larger washer and top up with distilled water to the mark. You don't actually have to handle acid at all, and even if you do get it in your hands the worst you'll get is slightly sore skin, and even then onlymif you don't wash it off straight away. There's really nothing to be scared of.
SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm
There are also little "L" shaped fluid level markers indicating the correct point to top each cell up to, that makes it easy to gauge the right level. If the fluid level drops below the top of the plates, then the battery may not be recoverable.
I agree with what's been said. It's important to keep the level up and as it's a doddle to do, why wouldn't you?
With apologies to the OP for this hijack... I have considered using the abundant dehumidifier water produced at home instead of commercial distilled water for the battery top up. Any problems with this?
#19: That's what I do. No problems at all.
Presumably dehumidifier water is ok to use for diluting coolant too (instead of demineralised water)?