I believe you were the one that referenced the Canadian repair shop that cited which side the failure is most likely to occur? I have no personal experience since I’ve never had a Subaru head gasket failure.
As to whether a poorly maintained battery venting acidic waste so close to the gasket and the radiator has any affect on the corrosiveness of the coolant again I have no personal experience. But it would seem to make sense.
I believe that Canadian guys are doing great job in helping their clients, they really put a lot of honest effort into getting these engines reliably restored.
I published the link to them before on this forum, can probably find it again in 5-10 minutes, but you pretty much followed their narrative, so I assumed you’ve read it.
Still, I think they are sticking to some urban myths, which can not be explained logically.
On another side, out of these myths, they make correct decisions, like making sure that battery terminals and engine grounding straps are very important to be in good shape.
Probably in Canada climate they see a lot of cases with these connections in need of attention.
This is not necessarily Subaru specific, but is a good practice in general, failing connections there make for quite hard to diagnose problems in electric systems.
Same, they make quite unsubstantiated claims about connection of battery outgassing and coolant system.
The problem of this argument is that coolant system is hermetically sealed, so the chances of having any correlations are slim (read “not existent”).
Still, it’s a good thing to make sure the charging system is not “boiling” the battery, so keeping attention on this topic is quite important too.
here is that Canadians web page: https://allwheeldriveauto.com/subaru-head-gasket-problems-explained/
I happen to bookmark last time I found it, still it’s quite old, dated 2007
There it is, I knew I read the same somewhere. You would think these guys have dealt with a number of these failures in their repair shop on older Subarus to know which side they are repairing most frequently.
I would agree there’s no way to prove direct causation. But it’s still a bit troubling if they are almost always working on the driver’s side.
And it is an older article so if you have a newer 2010 Subaru like the original poster and have properly maintained it you should have no worries about head gasket failures, at least no more so than any old vehicle.
Suffice it to say there’s no harm in properly maintaining your car Subaru or otherwise.
+1 
When I owned my Subies, I slept better at night if I maintained it to the spec… but that my paranoia moved to other brands I own too
They explained by saying that currents are flowing, the radiator is close to the battery, etc… etc…
The trouble is that radiator is NOT connected anyhow with chassis and thus it would not make for some current flow in the coolant itself.
I pretty much smiled and skipped all that arguments… they had a lot of factual data and they were recommending proper things to be done, both for repair and for the maintenance, this was the thing to get from their story
I owned an Audi for awhile, some cars are just beyond help. My Porsche was surprisingly reliable but I sold it before its fifth birthday so who knows how the subsequent owner made out. My Subarus, even the turbos, have always been about as reliable as any of my Japanese cars which is to say pretty much trouble free.
The head gasket issues as stated earlier are pretty much overblown for any recent vintage Subaru, as long as you care for your car.
PS: just because you’re paranoid doesn’t mean the car problem gremlins aren’t out to get you. Better safe than sorry. 
Haha that article is complete and utter nonsense! It reads like a conspiracy theorist’s explanation of why the earth is flat.
Car batteries don’t vent acid. Car batteries don’t even vent gas unless you have a serious charging problem.
But mainly they don’t vent or emit in any shape or form, acid.
then you will have to make a good explanation why any battery installed not under the hood typically has a special vent tube diverting these gasses outside - you will find these in Prius, Honda Insight, BMW and in generally in any car where battery is in the trunk or under the central console in the cabin
I’m not saying it is a lot of outgassing, but it is a part of the normal battery operations
if you have AGM battery, that’s a different story, they typically recuperate most of the gas, but even for them it is a pressure relief valve in place
And for the record, I’ve owned 7 Subarus including early 2L single turbo, several 2L twin turbos, 250GT 2.5 non turbo, 2L twin cam non turbo, 2.2L non turbo all from years '89 to '03.
Kept swearing off them precisely because of the intermittent oil leaks onto manifolds and one (the 2.2) that is the only one that actually had a failed head gasket. But kept buying them again. Haven’t had one for 12 years but will likely get another because they are great all round cars and, like the OP concluded, they ride superbly.
Here in NZ too, they are simply everywhere. Parts are plentiful and every corner garage knows them as part of their customer base.
Of course there’s a good explanation. When a battery is overcharged it vents hydrogen & sulphur gas. Without the vent the battery could potentially expand and rupture. A battery in the engine compartment doesn’t need to be vented outside (it already is) but one in the trunk or other “interior” part of the car should have a vent tube routed through to the exterior.
But to reiterate that article claimed the battery emits acid to the point of it coating the top of the battery. It then claimed this acid was being drawn into the coolant expansion tank. The most apt part of their explanation was “without getting to [sic] far into the scientific end of it”. No indeed. Their whole story was definitely without that.
in my comments above I pretty much make the same point that the battery/acid part of the article is quite questionable
still, they do have some water in the factual data what kind of failures they observed, how it corresponds to the gaskets design, how turbo engines gaskets are very different in design and tend to work much better, etc…
Indeed that is the experience here too. Was actually, on Wednesday just gone, chatting with my partner and her mechanic (yes, hers. We have different mechanics!) about fitting-in upcoming prepurchase inspections for a car she was considering buying. We talked about Subarus and his 2 comments were only buy the turbos because of the manifold designs and how it relates to the heat problems of non-turbo engines and not to get a CVT version. Luckily she only buys manual transmission cars.
Just an observation about batteries from my 60+ years of maintaining cars, heavy trucks and buses. Things near the battery corrode. In our salt rich winter climate near buffalo NY things always corrode but things near the battery corrode more. If the crud that forms on top of my batteries, irrespective of the make of battery or vehicle contains no acid, why does it foam up when I put baking soda and water on it? I don’t find the need to postulate a theory to explain why it is,
I am content to believe it is, based on observation.
As far as Subarus having more head gasket problems than other makes, I see more Subaru head gasket posts here than all other makes combined. Rather surprising given their small market share.
I’ve only owned 3 Subarus, first was long before the head gasket issues, next two both had head gaskets replaced, a 1995 legacy wagon and a 2005 outback wagon. Of all the cars I’ve owned, those are the only ones to ever have a head gasket issue.