Yes, it's dead, you need a new one.
They are prone to the silicone diode breaking down, allowing AC power to be delivered to the battery. Even then, the charging system is exceedingly weedy at the best of times, best not to use the headlight unless you need it.
I've been over these problems with the wifes YB100 and I eventually swapped out the silicone diode for an pattern honda 6v reg/rec as fitted to some C50/C90s. You can also get an excellent (but pricey) mosfet reg/rec from electrex. This has massively improved the charging system but does take a reasonable degree of electrical knowledge to fit.
I also replaced the standard bulbs with high quality LED ones and an electronic flasher relay to make sure they flash properly. These will flash with a much reduced power input and these ones in particular are very tolerant of a "dirty" power supply with fluctuating voltages and polarity.
I used these bulbs:
https://www.classiccarleds.co.uk/produc ... arth-or-ac
I used this relay:
https://www.classiccarleds.co.uk/collec ... -p-2-3-pin