Boot loop + battery of Picopix MaxTV (PPX720)

I have bought the Picopix MaxTV (PPX720) in early 2022 in Hong Kong.
The quality of the projector is pretty good initially and I was quite happy until mid 2023.
In mid 2023, the projector’s battery failed completely and I can’t even turn on the projector at all unless I am plugged in (i.e. I cannot charge the battery at all).

Once I plugged in, the projector enters a boot loop, as shown in this video

I finally managed to find a way to bypass the loop by clicking the bluetooth button at the back of the projector first before turning on the projector, in which the boot loop will resolve after 1-3 times usually, so I can still use the projector luckily.

I emailed Philips in Sep, 2023 and ask for help. They said I am out of warranty already as Asia’s warranty is only 1 year and they ask me to find someone on my own in Hong Kong to fix it. (This is quite heart-breaking to be frank as the projector cost 800 EUR and I am quite sure it’s probably a battery defect). Anyways, I reckon this problem is due to a battery issue, so I asked for the specifications of the battery that they are using.

The reply from Philips is

  • Length and width 115 x 120 mm
  • Height between 9.5 to 10 mm
  • Load 16500mAh

I tried looking for one online with these specifications but it’s quite hard to find one.
I came across the manual of PPX720 just now again and I noticed that the battery is 21000mAH as documented in the manual.

So I would like to ask, are the specifications of the battery mentioned above true or not? If it’s true, where can I buy one online?
Anyone here successfully replace the battery of PPX720 on their own? Is it more or less similar as in this video posted by Philips?

P.S. I have seen loads of battery issues here for this Picopix line including bloating of the lithium battery which is quite dangerous for me. So I think unless they fix this lithium battery issue, I am not going to buy one again.