I'm an engineer so I'm not afraid to take things apart to fix them. A quick google search revealed that others have replaced their shaver batteries and it usually requires a bit of soldering knowledge. No worries; I'm pretty good with soldering. If you're not, stop here because you won't want to do this yourself. If you want to do this, order your batteries from eBay or Amazon and come back when they arrive.
Now you have your replacement batteries and your shaver. You'll need these tools:
As oriented in the photo above, start to pry apart the bottom first. The top is held captive by the beard trimmer attachment -- both in open and closed positions. To remove it, the beard trimmer wants to be about 1/4 to 1/3 open. In that position the back cover can be slid down and out to remove.
To remove, I grasped the batteries at toward the bottom (charging plug end) of the shaver and pulled up. They were then held captive by the leads at the top. I marked polarity on the battery holder (+ and -) so that I would know the correct orientation to reinstall. These battery tabs are spot welded to the top of the batteries. I didn't have a cutting tool that would get in that small space, so I used a pair of forceps to pull/rip the tabs off the batteries. Start at the top and use force, being somewhat cautious not to pull the tabs completely out of the shaver. The goal is to remove the tabs from the top of the batteries -- and leave the tabs still connected to the shaver under the battery holder.
It is a nice feeling when they're out, isn't it?
The white batteries are the replacements. I marked polarity on the pack so I'd know which way to reassemble. Usually the positive end is covered by more tape, leaving a smaller diameter showing. To be sure, I checked with a multimeter -- and it confirmed what I already knew :-).
I suggest roughing up the contacts of your new pack with some sandpaper and tinning the leads. Without this step, they'll be harder to solder. Holding the new battery pack in place for soldering also proved a bit tricky. I balanced the shaver using plier handles and used another pair of pliers to hold the pack in place.
Soldering wasn't easy and took both hands, so no photos of that :-). Once you're done soldering, you can push the pack into the shaver. You'll need to fold up the leads so they don't protrude above the battery pack. This photo isn't the greatest, but I think you'll get the idea from it:
Now, see how close the leads get to the metal mount for the back cover? If the batteries are charged and contact that metal, a dead short will be created -- which is a "Bad Thing". For peace of mind, I put a few layers of electrical tape between the leads and the metal mount.
As an engineer, I'm a "function over form" guy, so aesthetics didn't matter to me. I'm sure you can make it look nicer than I did.
Now, it is time to reassemble. First, clean off the rubber gasket around the shaver. We want it to be clean of dirt and particulate so that it will continue to be water resistant. If you have a bit of silicone lube handy, put a light coat of it on the gasket for enhanced water resistance. Then fit on the back cover. Start at the top where the beard trimmer attaches. Push it to the 1/4 to 1/3 open position, then fit it down and toward the top of the shaver. When you've done this part correctly, the rest of the cover can be almost dropped in place. It should sit easily on the shaver body with no force required to hold it down. If force is needed, you probably don't have the trimmer correctly positioned. Now, put in the screws and you're done. Go plug in the charger and you'll be ready for a week's worth of cordless shaves -- or more. Good luck!
