It blinks whenever the battery is disconnected and reconnected.
I did however, just discover a fix.
For the 7.4v do this:
Unscrew the (extended) bottom cap from the body a couple times
Drop a metal battery charging spacer in from the top (plus side up, shake it if you need)
Drop your two tiny batteries in
Compress the batteries by screwing the top down the whole way
Now screw down your bottom cap until you feel it snug up on the batteries inside
The fix for the 3.7v long is a bit trickier:
Since the battery charging spacer is too thick
We need to find washers that fit around the bottom cap's center post
I found some great ones that were labeled 10-32 that measure 5.2mm ID and 12mm OD
But anything with a center hole larger than 5mm and a diameter of less than 14mm should work
Now stack them on the center post so the tip sticks out like the charging spacer tip (5 washers for me)
Load batteries from the bottom this time, screw the cap down until it snugs up
If the cap screws down all the way add more washers, you want it nice and snug on the battery itself
Your hvd lock function will now work