If you are looking for batteries for the A2 you have just acquired, you need Lithium primaries, not Lithium-Ion rechargeables. Li-Ions have a higher voltage which would be likely to damage the LED ring in your light.
The size you need are CR123A. They are 3V cells. The best ones are Surefire's own brand, which they call SF123; good alternatives are Duracells, and there are some other well-known and reputable brand names made in the USA which are OK.
Do NOT buy cheap cells, even though you will see numerous adverts for them. They are a very false economy and can be dangerous. And NEVER buy ANY cells on eBay.