Can you root? If so then why not try Lineage OS. The phones seem old and a lighter OS wouldn’t hurt. For battery you can try ACCA (requires root) or Accubatery Also depends on region but 3G gets taken down. WiFi and internet are dependent by tower distance and by how many WiFi clients and networks are around. Try WIFI widget handy tool. Cpu-z to check clock and thermals, ram usage and clocks. I do recommend installing Lineage OS and there are magisk modules if you’re willing to try, they might work they might not.