If you want to have lighting always on and have a high polling rate you're probably looking about a week or two of battery life tops. Either way, it seems like it's somewhat unusable unless you only have one profile and never switch between profiles. I think the problem might be due to the High Efficiency Mode reducing the power of the transmitter in the mouse or perhaps it's just a bug in the software. So far it seems to preserve battery life just as well and I would estimate a few months of battery life when used this way.

I did some troubleshooting and the only thing that would fix the problem was turning off High Efficiency Mode on any profiles and manually turning off lighting and reducing the polling rate. To reconnect I would always have to turn the mouse off and on and sometimes take out the batteries. When I started a game or exited a game and went back to the desktop the mouse would try to automatically switch profiles, but it would always become disconnected and never reconnect. The mouse worked perfectly fine most of the time, but it had a really hard time switching between profiles. I set up two profiles on my mouse, one for desktop use and another for FPS games in which High Efficiency Mode was on for the desktop profile. The concept is great, but in practice it has some issues. Speaking of battery life, there is a feature in the Engine 3 software called High Efficiency Mode which turns of lighting and reduces the poll rate to increase battery life. The RGB lighting is a nice touch, although I personally don't use it in the interest of preserving battery life. The side buttons are also on the smaller side which I like because it's not as easy to accidentally press them. The first thing I noticed after taking it out of the box was that the buttons were a little quieter than I was expecting and the scroll wheel had a nice firm feel to it compared to my previous mouse. You can even use it without the software if you'd like. Setup is super simple, basically just plug and play. It's definitely not the lightest mouse out there, but you do have the option of running just one AAA battery so it's around 90g instead of 108 with two batteries. The size is spot on, not too big or small, it's just as smooth as you'd expect it to be, it has dual wireless functionality, and tons of customizability using the SteelSeries Engine 3 software. I consider myself a casual gamer and I really enjoy this mouse after switching from Logitech.

Steelseries rival 3 dpi