Rechargeable batteries do have a much longer lifespan than regular batteries because regular batteries you can only use once and then have to dispose of them so the regular batteries will only last until you use the charge in the battery.
With rechargeable batteries you can recharge them once the battery charge as drained and then reuse those batteries over and over until they go bad.
Depending on the quality of the rechargeable battery you can typically get between 500 to 1,000 recharges out of a rechargeable battery before it won't take a charge anymore.
So while rechargeable batteries do cost a bit more than regular batteries you actually save money overtime because you don't have to keep buying more batteries when they go dead.