I'm sure a lot of people will jump on the "no, you're right, contend!" because real talk - if I'm going to use a lemon battery to run a toy car, why would I add a voltmeter? What would be the purpose? I might use one in the testing stage, but after that, who gives a shit?
However, be careful of arguing with her for the sake of more marks that won't add much. Let's say this SAC turns your 87% to an 88%. That's a 1% increase to your study score, right? Not true - this SAC will only count for half of your unit 3 mark, so it's 0.5%. BUT, unit 3 only counts for 20% of your final mark, so it's 0.1%. If your mark increases by more than 1%, then multiply it by 0.1 to get what the final change to your final mark will be (not even your study score - this is the mark that affects your study score, the change in your study score is likely going to be even less than this)
However, what if you push your teacher to the point that they don't like you? All of a sudden, they judge your tests more harshly because they're annoyed. They're less willing to give you help later. They make your experience in class annoying and a hell.
It may sound silly - but pick your battles. Don't go in arguing for more marks, go in with questioning. Maybe you lost those marks because the question was worded in a way that required a voltmeter, and you missed it? Don't make it sound like the teacher is wrong and you deserve the marks because you worked hard and you're right and she's wrong - try and approach your teacher with a bit hint of, "I want to do better on the next test, can you help me figure out what I'm doing wrong this time?", and it will make all the difference