There are two main steps, first one is to get green LED light by having + and − contacts placed correctly (+ is on the right side of the used battery “holder” (I might reopen this holder to show how I put together connections, just ask). After first step completed, please connect purchased 4.20V power supply to the 230V mains and let your Librem 5 battery charge (only if not already at 100% 
), until you get steady green LED light again. I’ve used following components (to “glue” things together):
− https://www.aliexpress.com/item/32696551544.html
− https://www.aliexpress.com/item/32976144021.html
− https://www.aliexpress.com/item/1005003701670611.html
@Lvovich, concerning the another replacement battery for your Librem 5, when and if interested user from Europe (I guess), please search this Forum for the other somewhat related post of mine, as of today, referring to “Designed in Germany”.