Real time graph of the temperatures and storage

[scidam]

T1 and T2 are floats, not lists. You are trying to append a value to floats, this is why the error raises.
At least, try to replace

T1 = float(string[0])                 #Convert first element to floating number and put in T1
T2 = float(string[1])                   #Convert second element to floating number and put in T2
T1.append(T1)                            
T2.append(T2)

with

T1.append(string[0])                            
T2.append(string[1])