Could you please elaborate why? thanks!
When it comes to batteries, there isn't really alot to ask of them. But the things we DO ask of batteries are quite important. Namely, people generally want:
1. A battery that lasts a while. This is particularly important with disposable batteries (primaries) vs rechargeable batteries (secondaries), since you have to buy new ones when they go dead. And when it comes to lasting, 'heavy duty' batteries are pretty much at the bottom.
2. A battery that can deliver high current with minimal voltage sag is also desirable. Generally, batteries that are rechargeable are better than disposable batteries when it comes to high current capability. But even among nonrechargeable batteries, 'heavy duty' batteries come up REALLY short.
3. Stable discharge voltage is also considered desirable, especially in cheaper, nonregulated lights. A stable discharge voltage means that your light will maintain brightness as you use it rather than getting dim as the battery discharges. Again, rechargeable batteries (especially NiMH) do better in this department. And once again, 'heavy duty' batteries come out on the bottom.
4. Maintaining capacity when heavily loaded. All batteries experience loss of capacity at higher loads vs lower loads. But some do more so than others. Once again, rechargeable batteries excel here. But even though the performance of alkaline batteries is pretty deplorable in this department, 'heavy duty' batteries are even worse.
The bottom line? Unless all of your batteries are dead and you have NOTHING ELSE available, stay away from heavy duty batteries! Rechargeable batteries (in your case, NiMH for these lights) are generally going to give the best performance. They're also the most economical choice for a heavily used light. Alkaline batteries are not going to perform as well. And 'heavy duty' batteries are HORRIBLE. If your light uses AA or AAA batteries, Energizer L91/L92 lithiums are an option. They will give you performance that is closer to NiMH (vs alkalines). But they will last longer in an intermittently used light. However, they are expensive and nonrechargeable.