So I found a great deal on a new Cygolite Miticross 350. But it looks like the item is from 2009. Will this affect the battery, brightness, etc? I bought a 2yr old Cygolite Hi-Flux used and it doesn't seem as bright as it's 150 lumen output, more like 100 even without the wide-angle lens. For $150 is it a good buy or should I just suck it up and pay full price? Again, the light is being sold on Amazon as new but the date is 2009.

The battery can not get "newer." So its possible that the battery's overall life may be shortened. How much the battery differs from a recently manufactured battery would depend on how the battery is stored. Most likely it was stored "correctly" and probably will work just as well.

Most Li Ion lights use circuitry that keeps the light as bright as possible for a given setting. When the battery fades, usually the light just completely shuts off.

If you only use your light a little bit, you should buy lighting setup that includes a recently manufactured battery. Otherwise it doesn't matter