Its using 2xAAA at 1.5V so the yellow led will only flicker when using a minimum or 3V
when its using a 1x1.5V Energizer + 1x3.7V the yellow led stays on indicating the laser is at maximum power. if using 2x1.5V the laser will stay on and will be around 300mW or 400
I'm going to go ahead and say using different type of batteries together is unsafe. A standard alkaline battery is going to be depleted much sooner than a Lithium cell.
This is taken from duracell's FAQ site.
CAN I MIX DIFFERENT BATTERY TYPES?
No, different batteries are designed for different purposes. Mixing a lithium battery with an alkaline battery will not improve device performance. In fact, it will reduce performance and may even damage your device or cause battery leakage or rupture. As well, do not mix different battery brands within a device. Doing so will reduce overall performance and may also cause battery leakage or rupture. We recommend using the same type of batteries within a device. https://www.duracell.co.uk/en-gb/faqs