my laptop ventilation and battery issue

hi everyone

my laptop have two issues 

• first battery issues 
• from about month ago i found my laptop battery not last more than one hour 
• i make service diagnose test from dell website and i found that battery its time to replace
• i went to service centre to check battery health 
• they informed me that battery is damaged and get swollen and must be change to avoid anyone effect on your device 
• i changed my battery and get another battery 
• my question why this problem happen how my battery get swollen in spite of i charge battery well and discharge it from time to time and i found power disconnect from battery after full charge
• also what is the best way to keep my battery safe to avoid get swollen again and your recommendations to prolong  my battery life span .
• my second issue about my laptop VENTILATION
• my laptop when playing games or watching high quality videos i find high fan noise and high temperature from the back side 
• also i found open gates for ventilation but there is no bleed air coming out of laptop however i put my device on glass table not on my lep or carpet something may an good ventilation 
• i want to know is that normal ? no ventilation and this high temperature .. and is these temperature may affect my battery again ??
  
  my laptop 5570 
  16G RAM 4G RADEON TM530 
  
  
  
  thanks for help