I'm not sure of your financial situation, but if you are eligible what about state or local medical plans like medicaid
You can always ask the mfg if there's help available for people in your situation also - some drug mfg help patients who can't afford it. There may some money available through alternate places also.
I know here you can't be turned away from the hospital for care - if it comes down to no help; I'd go in and have it done and let them know you don't have insurance and need a workable payment plan.
My PM/ICD (Boston Scientific) shows almost 8 years left on battery life - they projected 7-10 years.
I would contact the pacemaker manufacturer and explain your situation. I would think that there are ways to deal with your situation, I'm sure in the last couple of years there are thousands in your position. If you don't make progress with the manufacturer, contact your closest hospital. If help isn't offered there, contact your State Medical School.
Regardless of one's politics, this is a classic case for the need for health care reform.
Your battery can't be changed, as Ireneo mentioned, a new one will replace your old one and just the leads will stay in place. Depending upon how much of the time your pacemaker controls your heartrate, pacers last between five and ten years, I'm told.
Please... do some legwork. The card that you carry should list the manufacturer, start there, and keep us informed. There are very informed people who monitor this site and could offer suggestions.
My Dad's ICD had a beeper. Honestly! Of course under normal circumstances your cardiologist would be monitoring your pacemaker, doing an interrogation of the unit and could track the battery life. My Dad had his changed before the beeping started. But they bagged it and gave it to him and eventually the beeper did start going off (just a tiny beep every now and then). He had to stash it some place until the battery actually quit.