Sony TMR-RF810R Wireless Headphones Not Charging After Long Period of Non-Use

Hello.
I have SONY wireless headphones as in the subject, which I have not used for 3 years.
As I have a small child, I recently decided to "resurrect" them not to disturb the TV (small apartment) and unfortunately I encountered a problem.

I already charge them for about 24 hours and the lamp at the station is still red (after charging it should change to green).
The headphones are in "OFF" mode as per the instructions should be charged.

After disconnecting the headphones from charging, I change the mode to ON and the LED should light on them - nothing is lit, there is no sound either.

I wonder if after such a time without using the battery placed in the headphones got off, but as the new one costs about PLN 40, I decided to ask you, maybe anyone has any idea how to deal with it?

Should the headphones charge until resistance, in the sense of leaving them for some time? or maybe replacing the battery?
The battery is BP-HP550-11 / 2.4V 550mAh, maybe someone knows a reliable replacement?

Do you have a meter to measure battery voltage? However, after such a period of non-use there is a high probability that the battery will be replaced.

Unfortunately I don't have one. I would like to add that I used to use headphones a few times during the 3 months period, then I put them in the cabinet.
The manual says that the first charge should be connected for 16 hours, so I delude myself that maybe after a long charge they will work ..: /