Ya ambient temperature plays a huge role in battery testing, both for the battery itself and in the case of a toaster, the element's benchmark ambient temperature. What that benchmark (testing) temperature is depends on the tester model. You could also overheat/damage the element if you run multiple tests sequentially. Those two reasons are why you must allow the element to cool off completely before the next test. Some electronic testers will also ask you to input an ambient temperature range in which you are performing the test as temperature affects a battery's performance and internal chemistry thus affecting an accurate reading if not compensated for in the measurement.