I think i found it (the charging circuit). And i also found a diode that's gone bad on that board. Measures continuity in both directions.

So i have this UPS Cyberpower OL2000ERTXL2U that is no longer charging the batteries and i would like to try and figure out if its fixable ? It did throw up and error message on the LCD saying Charger Failure and so i powered it off and back on again and it no longer shows the error and seemed to be fine. But the batteries just go flat now and it dose not show any errors other than batteries low.

Have taken some pictures but i dont know where the charging circuit is or what parts to look out for to replace. Everything looks good. No swollen or leaking caps. No burnt or discolored...