Norelco shavers usually have a great battery life. You eventually just have to charge them more frequently and more often until the battery itself is completely dead and un-rechargeable. At this time you can either decide if the blades are dull enough to buy a new shaver or to replace the batteries in it. Replacing the battery in a Norelco shaver is an easy task with the proper tools.
Slide up the sideburns trimmer on the shaver.
Try the various torx head screwdriver sizes to find the fit for the two screws holding the top of the back shaver cover on. Unscrew the two screws that are under the sideburns trimmer that hold the back of the shaver on. On some Norelco shavers, the back will now slide off if you apply downward pressure on the shaver's back. Other Norelco shavers have one or two torx screws on the base of the back cover on the shaver; if so, unscrew them also. Place the screws in a safe place.
Take the back cover off the shaver. Some shavers may have a strap fastening the battery down. Unfasten the strap if there is one. Take out the battery.
Replace the old battery with a new rechargeable Ni-Cd AA battery. Re-fasten the battery holding strap if there was one.
Replace the back shaver cover and re-screw in all the torx screws,