Motor turns over slowly with key

Motor turns over slowly with key

Usually starts the first time OK, but after I empty the bag and try to start it again only a minute later, it turns over once/second. Starts on 2nd pull of the retractable, but I have an elbow injury that makes it difficult. I've replaced battery (no change) and will replace the spark plug for giggles, but is it more likely the starter motor or a bad battery?