I've been using the Streamlight SL-B26 rechargeable batteries for my ProTac HL-X flashlight, and they've completely transformed my experience. The built-in Micro-USB charging port is incredibly convenient - no more fumbling with external chargers. Just plug in any USB cable (though I wish it was USB-C) and you're good to go.

The battery life is impressive. During a recent camping trip, my flashlight stayed bright through three nights of heavy use. That's a huge improvement over disposable CR123As I used before. The dual-fuel compatibility means I can still use regular batteries in a pinch, but I haven't needed to since getting these.

Charging does take about 5 hours, which feels slow when you're in a hurry. But the trade-off is worth it - these batteries hold their charge remarkably well even after months of regular use. I particularly appreciate the safety features that prevent overcharging; it gives me peace of mind when leaving them plugged in overnight.

The only real downside is the size - they don't fit all flashlights. They work perfectly in my ProTac but wouldn't fit an older PolyTac model I have. Still, for Streamlight X-Series users, these are an absolute must-have upgrade that pays for itself by eliminating disposable battery costs.