Why can't I change or repair the battery ic

Batteries made within the past ~10 years are a gamble as to if they are rebuild friendly. There are some that it isn’t a big deal on and the BMS will try and make it work, but others like Dell have become significantly more difficult because they were hit hard by the Sony recall. Dell also shut the site down so you cannot check anymore outside of referencing the list of known bad ranges and treat all packs in that range as bad. It's better to replace it for proper insurance against the recall - that even applies if I only intend to use it for old XP era games for example. You have to replace the BMS with Dell laptops on post Sony recall packs and the newer models like the E Series.

However it is still possible if you know the BMS is receptive to cell changes (and will try and charge bad packs). Many of the older HP batteries will attempt to charge it unless it has a problem like cell rust, but this can be dangerous. I was testing a pile of 7 nc6000 batteries after I rebuilt some of the better laptops so I can pick a nice candidate for older games to receive a hard drive. 2 of the batteries had shorted cells and the battery didn’t stop charging. These are inherently excellent to rebuild, but can be dangerous if there’s a problem with the existing cells. If you have a battery like this, you should at least do 1 complete supervised charge to catch major pack problems like cell shorting. Beyond that, 1-2 additional supervised charges is recommended to stabilize the BMS data and be 100% sure the battery is not bad.