Why does using different units but same physical value give different result?

Question

I'm trying to define a variable with the value of the thermal constant $V_T$. The value of the thermal constant is given in Volts as $V_T = \frac{k T}{q}$, where $k$ is the Boltzmann constant and $q$ is the charge on an electron.

Why am I getting different results from the following two inputs:

k = Quantity["BoltzmannConstant"];
q = Quantity["ElementaryCharge"];
T = UnitConvert[Quantity[25, "DegreesCelsius"], "Kelvin"];
Subscript[v, t] = UnitConvert[(k T)/q, "Volts"]

Which is returning the expected value of Quantity[0.0256926, "Volts"].

k = Quantity["BoltzmannConstant"];
q = Quantity["ElementaryCharge"];
T = Quantity[25, "DegreesCelsius"];
Subscript[v, t] = UnitConvert[(k T)/q, "Volts"]

Which is returning the unexpected value of Quantity[0.590610, "Volts"].

The only difference between the two is that in the first one I convert the from Celsius to Kelvin; however, the inherent physical value is not changing. So when I convert to Volts, shouldn't I get the same result from both inputs?

Answer 1

Correct Temperature Conversion Code

k = Quantity["BoltzmannConstant"];
q = Quantity["ElementaryCharge"];
T1 = UnitConvert[Quantity[25, "DegreesCelsius"], "Kelvins"];
Subscript[v, t] = UnitConvert[k T1/q, "SI"]

(*Quantity[2.56926, "Centivolts"]*)

Answer 2

I contacted support and they said they were "able to reproduce the issue." It seems like this is unintended behavior and will be fixed.