iphone 7 Plus crashing, rebooting to 10% battery

I am suddenly having an issue with my iPhone 7 Plus crashing. It typically happens when the battery is somewhere below 50% and usually when starting a new app. (I've been keeping running apps to a minimum while this is happening). The batter will be at 40% (as an example), it will crash and reboot and when it comes back up is at 10% battery life or less. I plug it in and in a few minutes it returns to the previous battery level prior to the crash. Battery health shows at 74% and says it should be replaced. Is that the root cause or would that not do this? (Needless to say my batter does not last long.) I really don't want to buy a new phone right now and will get a new battery if that seems like a fix for this but if something else is wrong I don't want to waste the money on the battery.