I do understand now that most of those safety concerns apply not to regular Nimh rechargeables.
I take from this that you are using rechargeable batteries. Also, AAA batteries (both rechargeable and non-rechargeable) are very safe. Alkalines leak and lithium primaries can catch fire if physically damaged, but that's about the extent of it. NiMH are rock-solid and will never do anything dangerous without your explicit intention.
The Tikkina, as far as I'm aware, is not current-regulated. In fact, I don't think any of the 3×AAA Petzl lights are regulated. The company has been using cheap, outdated electronics for many, many years. Also, forgive me if I go on a rant—this is a pet peeve of mine—but their runtime reporting policy has been exceedingly dishonest if not outright cancerous for the industry. E.g. for this light in particular they claim "60hr" runtime for both the 100 and 150 lumen modes. This is both laughably impossible (there is not
nearly enough capacity in the batteries) and nonsensical (an LED can't consume the same amount of energy for a mode with 150% light output). The actual truth is that you get the maximum 150lm on a fresh set of batteries, which then quickly ramps down as they're depleted, and the vast majority of these 60 hours you actually spend within the range of the lowest mode, following an L-shaped output curve. An educated guess would put its
actual runtime at about 2–2.5 hours to 50% brightness, and that's being very generous and assuming the half-output is still useful for the task at hand. I remember the days when I was using non-regulated lights, and back then I felt the need to replace batteries long before they were completely drained just because the light was already getting too dim to use at that point. Thank god we've had fully regulated headlamps on the market since, uh... what, 2010? Petzl has had enough budget to get on with the times, yet they choose to deceive their customers instead.
In short, I would suggest replacing the battery that dips voltage. It's probably faulty and/or has outlived itself.
(And then I would also suggest getting a better light, preferably based on a 1×AA current-regulated driver. Thankfully, there's no shortage of those!)