As noted, if you're having Vector 3 battery connectivity issues, the fastest path to resolution is:
1) Ensure you've got the newer battery pod holder design (this came out years ago, and Garmin sent it out to everyone for free years ago, but not everyone filled out the little form. Hit up Garmin support and they'll send them out to you for free).
2) Switch to CR1/3N batteries. The reason Vector 3 had so many battery issues is that the production of LR44 batteries varies greatly. They aren't as uniform as power meter companies hoped (Verve Cycling also hated their life choice after they selected this battery design for their power meters). So the lack of compliance caused tiny little disconnects, especially with 2xLR44's that can change size/shape over the life of the battery. It's why some peopel went years without a problem, and others couldn't catch a break. They bought different batteries at different stages of life. The new pod design essentially eliminates that.
That said, this is one of those issues that was literally solved like 6 years ago for people with Vector 3 (June 2018). So if you're still somehow having issues, and haven't done the above, then definitely reach out to Garmin support. Rally uses the newer battery pod/cap design, and battery stuff simply hasn't been an issue there.
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