Had my Cali’ since 2012. Never realised during my first few years of ownership that the battery needed to be topped up. Current ( pun😂) battery is 5 years old. Just put 50ml of distilled water into each cell to top them up.
I’ve checked the voltage with the engine running, it’s not overcharging. I put the battery on an Optimate once in a while, not left on all the time.
Question is do you have the same “issue”, bit of a faff to top up the cell under the tank.
Wonder if it’s the heat from the engine? I bought some self adhesive heat shield for my car. Wondering if there’s anything to be said for sticking some on to the sides of the battery box. The front of the battery is probably shielded from engine heat by the air box.
Or am I overthinking, as I’ve just retied and at the stage where tinkering with the bikes is my thing. 
Thoughts anyone?
Welcome to retirement zone
Top up wet batteries is a pain.
Some years ago, got so fed up having to top up the battery on my '66 Triumph that I chucked it out (responsibly, mind) and put in a gel type replacement. One of my better decisions.
Never had to do anything since apart from connecting it to the optimate once in a blue moon.
batteries lose a little through charging
its how they work
at 5 years of age, its likely to be near the end of its life anyway
I fitted a sealed lead acid yuasa to my machine, but that was specified by the manufacturer, and I didnt fancy a cheaper wet battery
buy cheap pay twice !
It may be five years old, still starts the engine easily. 
But, next time. 
45 years years in the trade
I am psychic
it will now die the very next time you use it
and you can blame me
You’re probably right. 
When my vehicles used to have batteries with plugs for topping up the water, checking the level ‘and topping up if necessary’ was part of standard routine maintenance. I think most owners manuals said once a week. Alternatively SLA’s have a reserve of fluid to allow for loss, but when that’s gone, sayonara, new battery time. Try to avoid overcharging SLA’s. 
Never had to top a battery on any bike or car as much as on this one.
I have also gone down the sealed battery route on my Cali, I think it’s called an AGM (absorbed glass matting) It sems to work well and is a lot smaller than the standard lead acid battery.
My T140 Bonneville does still have a wet battery. I checked that recently for the first time in a couple of years and found several cells to be very low on fluid. It has since been topped up and is still working, but I’m not sure for how long. It doesn’t have to do very much or work very hard as the bike doesn’t have an electric start.
Seems to be the case that a lot of cars have insulation around the batteries, read that some even have fan cooling. So, I’m guessing that heat is a problem. But in the grand scheme of things!
Its fair to say that engine/gearbox heat is only going to speed up electrolite loss via evaperation id just wait till the first sign of trouble then change it for an agm one checkout tanya batteries website(google it!) for a good selection at a fair price!.
good luck
Cheers, when it dies, that is the way forward.
I usualy just top my LM battery up when I service the bike. The Varta battery is 12yrs old and test out fine on my battery tester. I just use a CTEC charger one day every two weeks . Does the trick for me.