I own a Yaege FC-1 frequency counter. It is around 4 years old, and recently I noticed its internal battery is dead: No more than 10 minutes of autonomy. The battery was a 18350 / CR123A, so it should be easy to find a new one.
But recently I have had bad experiences buying batteries at eBay: All the batteries I purchased were dead, with almost no capacity and very high internal resistance (in other words, useless), so I looked for a different solution.