Hi there and welcome
The FAA allows this Sarah, you can read this here
For Spirit, A maximum of one spare battery not exceeding 300 watt hours (Wh) or 25 grams equivalent lithium content (ELC), or two spares batteries not exceeding 160 Wh (13.5 grams ELC) each may be carried in carry-on baggage.
So you are ok, as your within this
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