BLF A6 uses voltage divider to calculate battery voltage and the resistance of these resistors may changed between different versions of the driver.
TK has firmware to calibrate the voltage reading
https://bazaar.launchpad.net/~toykeeper/flashlight-firmware/blf-x6v2/files/head:/ToyKeeper/battcheck/
You can flash this FW and then flash back the A6 FW using the correct values in order to get 5 blinks.
after seeing the following chart from Toykeeper showing 5 blinks is, > (more than) 100% full I am satisfied that 4 blinks would indicate full and not over full.
(each blink represents about 25% of a full charge)
0 blinks: < 1% full (< 3.0V)
1 blink : 1% to 25% full (3.0V to 3.5V)
2 blinks: 25% to 50% full (3.5V to 3.8V)
3 blinks: 50% to 75% full (3.8V to 4.0V)
4 blinks: 75% to 100% full (4.0V to 4.2V)
5 blinks: > 100% full (> 4.2V)
I’ve had my BLF A6 for a long time; it has never blinked; how do I get it to blink?
Hidden Modes:
Go backward from Moon to access Hidden Modes, they are:
-Turbo
-Strobe
-Battery Check
4. + Bike Flash