Despite never having had any issues, I received an email from Garmin today offering me a free replacement of the battery door.
Might be worth checking your inbox/ spam/ junk if you use the same pedals.
Garmin recently became aware of issues with the battery contacts of returned Vector 3 units. It was determined that the swelling of batteries under normal discharge over time can cause the battery contacts to become compressed, which could result in power drops and spikes. This, combined with the shock and vibration experienced in cycling, could permanently deform the contacts leading to disconnects. The battery swelling does not present any safety–related concerns.
In an effort to improve the reliability and functionality of the Vector 3 system, we have redesigned the battery contacts and doors to prevent these issues from occurring. All Vector 3 owners can get free redesigned battery doors by entering the discount code below at Garmin.com.
Note: Vector 3 customers will need a quantity of two. Vector 3S will need a quantity of one.