Ice chest temp test

• Ice chest size in gallons: 12 gal (48 qt)
• With 2 carboys in ice chest, water needed to fill carboys to 3qt mark: ~5 gal
• Water temp from faucet: 68 F (kitchen ~72 F, outside ~55 F)
• Water temp from fridge:
• For room temp:  ~70F and ice chest closed, temperature rise per minute of water: 3 F in ~13 hours
• What's the effect of 1 16oz frozen bottle on water in closed ice chest? ie how many frozen bottles needed to maintain temperature? 1 bottle drops 5 gal about 3F