Replacement batteries should be available online; type 'BST-33' / 3.7V Li-Ion.

It's common for phone batteries to have a limited lifespan, more so than a charger; and if an original charger fails, it is usually dead with no output voltage, in my experience.

I was thinking that dead batteries should show 0V. And this one charges up to some voltage. But, ok. I will try with replacement battery.

Also, since this phone is 20+ years old, is there a way to unlock it from specific network for free?

It probably won't even have reception, most networks have already moved on from providing GSM/CDMA/3G and only support 4G/5G.

jmarsh wrote on 2025-02-09, 16:34:

It probably won't even have reception, most networks have already moved on from providing GSM/CDMA/3G and only support 4G/5G.

Once I have inserted correct SIM it worked very well, and made a call to test it

So I got replacement battery which is almost fully charged (3.9V) but when I try to turn on the phone, the red led blinks few times (same as with original battery). When I try to charge it, it also blinks few times like the old battery and nothing happens. Also the replacement battery has wrong label for polarity, + is actually - as vice versa 😁

What is the next I could check?

Update1: Can't find much on google but what it says that this might me EROM problem, which I have no way to solve. Data cable I could find, but software probably don't exist 🙁

It could be a connector problem (if not a battery issue or temp being too cold) according to Sony support:
https://www.sony.com/electronics/support/articles/00013415

There are a lot of more phone-oriented forums than this, with suggestions on firmware/software updating, unlocking etc.
E.g. avforums, lo4d, esato are just some such sites I found through google.
(Note tha many threads are dated from when the phone was almost new, so it might take some effort to locate current information.)

Rwolf wrote on 2025-02-10, 20:56:

It could be a connector problem (if not a battery issue or temp being too cold) according to Sony support: https://www.sony.com […]
Show full quote

It could be a connector problem (if not a battery issue or temp being too cold) according to Sony support:
https://www.sony.com/electronics/support/articles/00013415

There are a lot of more phone-oriented forums than this, with suggestions on firmware/software updating, unlocking etc.
E.g. avforums, lo4d, esato are just some such sites I found through google.
(Note tha many threads are dated from when the phone was almost new, so it might take some effort to locate current information.)

Thx, will try with those too!

I manged to fix the phone, by using data cable for it. I have installed software setool2_lite_v1.11 (free tool).
After I started the program (in windows XP), I have connected the phone and pressed the numbers 2+5 at the same time before plugging the phone. I tried the option recover but I didn't have ROM for it, but somehow only connecting like this was enough to make it to start again.

Thank you all for suggestions.