1997 Oldsmobile Bravada .. OBDI CODE P1870

Question

Have a 1997 Olsmobile Bravada. When to shop because check engine light is on. Code was P1870 .. Check engine light has been on for 8 years and I drive it but lately my battery keeps going dead and have to keep recharging the battery. 3RD new battery in the last year. My check engine light come on after driving on interstate but after about a week it goes off. But while it is on I can feel a delay in the power on the vehicle.