Good batteries are hard to come by nowadays. Most of the cheaper ones dont seem to last long. Even if they do , you'd be lucky to get 2 years of service from hem.

My dominar is on its 3rd battery (ytx 9) the stocker lasted an astounding 4 years and it was still working when I swapped it out as a precaution to protect the rectifier. The green Tokio battery lasted barely 6 months (80). Now running a yuasa battery (130). Hopefully it does better.

On the NK , I just bought a ytx14zt lithium battery as the stock battery is on its last legs, dropping to 9v on startup if left unused over the weekend. Best to have a standby battery.  Got it cheap from 6.6 shopee sale and some coin redemption. Paid 309 for it.

It is comically light though... But I bought it to offset some of the weight from my racks and panniers. My battery is mounted high in the tail so should help with bike balance going with a lighter battery.

If you are considering a lithium battery, bear in mind it does have pros and cons so it may not be suitable for all situations. Glad to explain if you guys want to know why.

Man...you paid 200 for that green turd. My tokio was 90.

That starting issue is a weird one. Notice if the crank speed is lower than previously? On my ytx9, it cranks slow, then fails to crank at all.  Like not pushing enough amps.

The battery in my Ninja 400 died the other day and not knowing better, I got it swapped with the green Tokiohama, even paid 200 for it because I had someone send and change it without knowing how simple it was to replace myself. Was in the middle of work and didn't have time to check my options. Not sure if it's just a crappy battery or poor installation, but now my bike weirdly has to be in upright position to start normally, otherwise I would have to crank it 3-4 times just to start the bike.

Another astounding bit is that my bike was manufactured in 2019 and registered in 2022, and although it's seen little use, it's miraculous that the battery last 6 years. It's a FTX9-BS made by Furukawa Thailand.

JustForFun
this is from manual, 14.5~14.9V. you should try to measure it. if this is the case, the bike cannot use Gel battery, the charging system will over-volt it and kill it within weeks

yours have the buzzing sound?
can you locate the source of the buzzing sound?
with the old battery also got buzzing sound?

suggest try troubleshoot the starter relay, maybe knock it a little bit like RoofTopPrince said

I have one, digital voltmeter for bikes, and a few in spares
wired to the headlamp bulb

what I did, was correlate the voltmeter reading, to the actual voltage at the battery, both when switching on, and then with the bike revved to 5k RPM or more
usually, the multimeter at battery will read more, let's say 14.6V, but the voltmeter, being further away, will probably read 14.1V around there

just keep in mind the difference, and live with that

I installed this 2-way USB charger and use it to charger / tender my battery with a power bank.

Scooter with plenty difficult to remove fairing is pain for DIY therefore gone for this solution.