Firstly, I assume you mean battery life in terms of degradation due to heat, not runtimes which will invariably get shorter as you increase output.
The BLF-A6 Driver was designed for the A6, which is a very similar light to the S2. It will get too hot to handle in the higher modes, but has thermal regulation you can set and will automatically step down at your desired temperature. A 8 x 7135 2.8A driver (like many stock S2 come with) is about the limit of what you can sustain wiithout thermal stepdown in the S2+. So if you use the 17DD driver, any mode that draws more than 3A is probably going to eventually throttle. 2.8A with a modern high output LED (XP-L HD/HI, SST-40) will get you over 1k LED lumens, possibly close to 1200 with an SST-40. You are unlikely to hurt either the LED or the cell running at that (assuming decent thermal contact between led>mcpcb>pill), though I wouldn’t leave it unattended on max output.
You are correct in that the thermal enhancements would only delay the throttling.
So, i guess there are a couple options for you. The simplest would be to try running a S2+ in the highest maximum factory configuration- 2.8A driver, LED of choice (though Luminus SST-40 is the best in terms of sheer output for a single die 3v LED, you do sacrifice CRI/Tint choices.) You should be able to hit well over 1k lumens without having a hotrod light.
You could also install a 17DD and give it much higher possible output, as well as thermal regulation so it will never overheat and damage itself. If you don’t need turbo mode, you can always run it on a lower mode to match the performance of your current configuration. Maximum performance with a FET requires special attention to LED and battery choice though, some LEDs will burn with high drain cells on direct drive regardless of heatsinking. Also requires springs to be bypassed with wire to reduce resistance.
Another option would be to change hosts entirely- It’s hard to recommend the S41 nowadays, the emitter choices are dated and stock factory output is rather low compared to what is possible now. The Jaxman E2L is a compelling choice for your use case, as it takes the form factor of an S2+ (though slightly shorter), and adds heatsinking fins to dissipate heat, as well has having an integrated shelf transfer heat instead of relying on the threads to transfer heat from a pill to the outside body of the light. Additionally, it uses 3 LEDs on a single board, which increases efficiency at reasonable levels (more light vs heat output at the same current vs a single LED) as well as much higher maximum output should you desire to run it at higher currents. The one thing to consider would be the optics layout, the E2L uses Carclo total internal reflection (TIR) optics instead of a traditional reflector in order to focus all 3 emitters. This will generally lead to a floodier beam than a single emitter would produce. The E2L is available from Jaxman’s aliexpress shop as either a host (Add 3x LEDs on a 20mm MCPCB and a 17mm driver) or as a pre-built light with about 900 lumens of sustainable actual output through the front. The downside is that the stock driver is quite simple, just a low-medium-high with memory. No worse than the old stock convoy 3/5 mode drivers, but there are more flexible options now with Bistro(improved A6 firmware), Biscotti, etc. firmwares available.
Isit worth it? That’s up to you. Assuming you have a 17DD right now and nothing else, the cheapest route is obviously to use what you have. The A6 firmware is nice in that you can roughly match the performance you have now (with very minor runtime loss due to a FET being less efficient than 7135s), and only step up if you need short bursts of higher output.
If you don’t mind buying another light, I think you can get a new Convoy S2+ with 2.8A drivers for around $12 USD and you can try it out that way. Make sure you get something with their new firmware though, not the old 3 mode one.
If you like the idea of a triple LED setup, the E2L is basically a premium S2+ designed specifically for 3 LED setups, and is really nice. As a bonus, it legos well with Convoy battery tubes so you could make it even shorter than stock with a 18350 tube and cell.
Otherwise, there are many other options. The M1 is a larger light, and a larger light will have more heatsinking mass, as well as larger dissipation area enabling you to run lights harder and longer without thermal limits. It really depends on what you want, there really are no wrong choices here. If you end up with something that runs hotter than you’d like, just step it back a mode and use it on a lower setting.
