I've had my two YS-D1 for quite a few years, they were serviced about a year ago.
With my EM1-MkII (which I've had for about three months) I have noticed a very annoying problem:
In certain circumstances the strobes drain the batteries with only a few shots (as few as two, but usually within about half a dozen strobe flashes).
Specifically, with the YS-D1 in TTL (optical trigger connection to my Nauticam housing), if the strobes are poorly aimed and aren't hitting my subject and the camera is in "fill flash" mode. My theory is that this causes the flashes to fire all out and something, something, no, I can't really explain it.
Broken batteries, right? Well, I tried with my trusted Sharp 2700mAh (I had used those for a few years), which I then tossed out because I thought they had finally failed.
Then I tried with brand new Eneloop PRO (fully charged).
Then I tried with a dive buddy's Eneloop (fully charged) - he uses them in his Inon strobes all the time).
And with off the shelf Panasonic Alkali AA.
And with Energizer Lithium AA.
With all five battery types I can reproduce the same behavior.
Now if I don't do that (TTL, fill flash, poorly aimed strobes), the camera/strobes work happily together for hours. Today was day six of this dive trip (also: last day) and now that I understand what causes the issue I took about 170 flash exposures over three dives (3.5h total) with no problem at all. Didn't change batteries between dives, one set of standard Eneloop and all was well.
Am I going crazy? I don't think so, but may not be a good judge here... my dive buddy observed the scenario multiple times over the past 20 dives (and helped out with loaner batteries) and couldn't figure it out, either.
Since I never had this problem with my EM5, (same fiber cables, same strobes, etc), I'm thinking it's "something" about the EM1-MkII (which I otherwise love). I'm planning to write Olympus as well, but figured I'd ask the experts here, just in case this sounds familiar to someone.