will leaving my flashlight(s) out in my car have a negative impact on their life span be it primary or rechargable?
It depends on the ambient temperature, but the overall answer is yes; extreme heat causes a battery to self-discharge faster, and extreme cold causes a battery to perform intermittently or not at all.
Most batteries are designed to withstand temps up to 120F, but a car interior in the summer has no problem getting up to and beyond 140F. A mild example would be a NiMH rechargeable that goes from fully charged to completely dead in a matter of days due to the heat causing high self-discharge. A worse example, an alkaline that swells and leaks, damaging your flashlight and possibly your car. The solution here is to use a battery type that best handles heat, and to keep your flashlight out of direct sunlight; Lithium primary batteries, such as Energizer Lithium AAs or 123 primaries, will handle up to 140F. And your completely dark glovebox or trunk will rarely, if ever, reach 120F.
As for the cold, once you get below freezing, most popular battery types will begin getting unreliable, and at around 0F they'll stop working completely. The key here again is a robust battery type, and lithium primary cells are rated down to -40F.
It should also be noted that Li-Ion rechargeable cells can become permanently damaged by extreme heat or cold, so avoid using them for car duty.
