Mechanical switch lights like the Convoy S2+ do not have any parasitic drain. But be aware that the batteries themselves have some self-discharge, Li-Ions are the worst at something like 5 percent in the first 24 hours and then loses 1–2 percent per month. Protected Li-Ions are even worse at 4-5% per month.

If you need to keep them stored for long periods, get an AA-compatible or dual-fuel flashlight and use Eneloop batteries for rechargeables, or Lithium primaries if you don't need/want to recharge.

Oh boy.. I initially read "fleshlight" and it got me very confused.

Yes, but....

There is much hyperbole about parasitic drain, and the sheer and utter necessity of mechanical lockout, but most lights have so little of it that the discharge rate barely changes when you do a mechanical disconnect, or even remove the battery. Ambient temperature will have at least as much effect.

If you place on just tossing the light somewhere and not using it except in emergencies, you want something that takes a CR123 or other lithium primary cell. However, if you're not turned off by having to at least check on your light 3-4 times a year, or if you actually use the light often enough to need to charge at least half as often as you'd need to replace alkalines, the discharge rate is low enough that it's not worth worrying about. Especially not unless you are the type to go to great lengths to ensure that your light never sees ambient temperatures above 20C/68F.

For lights that have aux LEDs, even the worst of them than I know of can last months, and most can last years. Then again, you wont' need aux lights if you're just chucking it somewhere where it will likely be unused. Turning the aux on High, may run some lights dead in as little as a week and a half, but there's really no reason to run them on High all the time. It's great to show off or mess around, but they're best not left on High. Especially not in a TS10, and double-especially not if you snag a first-batch TS10.

Whether you need to worry really depends on how you use it. Personally, I use my copper TS10 a lot, and despite it's short battery life (one-third what an 18650 gets), I'll still go at least a couple weeks between charges unless I get silly playing with Turbo. And it's usually well over half-charge despite the frequent use at low levels.

I'd worry more about remembering to get the Nichia version instead of the LH351D version.

Everything but lithium primary or eneloops in a light with a mechanical switch will have battery self-discharge (bonus: neither of these two battery chemistries leak). An e-switch adds a bit more parasitic drain, so the best bet for a light that won't be used for a long time is CR123A or white eneloops, and if you're not sure what the switch type is, you can just break the contact of the batteries.

Yes that's a thing with all batteries unfortunately. They discharge when not in use. It's not about the flashlight, but the batteries.