The V3 doesn't have a contact disk like the V1 and V2 had. It's a screw that makes contact with the battery.
What type of switch do you have in your V3? The original silver screw with several washers under it or the 3.1 brass screw?
If you have the original screw, make sure it's tight and put a tiny bit of Noalox on the tip. Also, make sure your
batteries have not become indented at the bottom. A few people have reported that happening with the Tenergys. Replace the
batteries if so. I also recommend you upgrade to the 3.1 switch. The new brass screw does not pit or tarnish and requires no maintenance. Plus, it has a wider contact area for the battery.