AT&T 1545 Question

I acquired an AT&T 1545 phone set with answering machine, and it came without the power wall wart (I asked the guy who gave it to me if he had the adapter, and he said he'd check, but it's likely he won't). I presume the wall wart is for the answering machine because the phone also has the 9V battery in the compartment for memory backup. I don't really need the answering machine, so I was wondering if anyone had experience with this set and if it will work okay - the LEDs and stuff - without the wall wart, or if it will run down the batery quickly. I don't want to have to feed it batteries every month. THanks.