Carrera Suntour battery issue

[OldManToy]

Hi everyone. I picked up this cheap battery with the aim of it being a reserve. It has around 80% charge and will power the bike Carrera Subway 2. Battery SOH shows two flashing lights. However it will not take a charge. I know the charger is good as it charges my other battery just fine.

Can anyone suggest how to diagnose the charging port and internal connector?

Also, morw for curiosity, any ideas as to what the small ON switch is in the pic?

Thanks, and be gentle with me as I'm a new to ebikes.

 

[Nealh]

Switch is likely for a reset.
Reasons for not charging a few;
SOC may be too high, try discharging a bit more to see if the charger charges. I have a generic charger that won't charge if SOC is too high on a 48v battery.
Internal charge fuse if fitted is blown.
Cell groups or a cell group is way out of balance/at lvc.