Review (3/5): Battery looks like it will, but does not readily fit the G290
I have this battery soldered in my old G290 and it is holding a charge like it did when it was first purchased years ago, so if you have a G290, it will work. But here's the problem-the image for this battery matches perfectly the markings on the stock battery in my G290, but the battery shipped is actually about an eight an inch larger in diameter (about same length; has almost no markings). Note that no dimensions are provided for this battery, so it's not possible to determine this in advance. If I didn't fear that I couldn't get the body snapped back again, I'd pull it out and measure it for everyone.
Anyway, here's how to get it to work if you want to revitalize your G290 and you can't find an exact battery match from Norelco or another vendor like I thought I had- to get the body open, take a cheap knife and carefully pry in between the two halves of the plastic body about 2/3s down the body from the top. I applied steadily increasing pressure and the two halves popped apart without damage to the little latches that hold the two halves together (seriously- be careful or you will end up with an open hand instead of an open shaver). Keep the on/off button in the off position! (When you re-assemble the halves, the power button needs to be off to catch a little switch that completes the circuit.)
Look at how the wires run along the side of the battery so you can route them the same way for the new battery. Carefully lift the existing battery up and out of the shaver body, taking care to not break off any of the wires. The wires go straight through the metal tabs on the end of the battery. Touch a soldering iron with a small tip to the underside of the tabs (the side with the wire sticking through) to release the wires- pay attention to which wire goes to the + and - terminals.
Now, pull out a pair of needle-nose pliers, ask your G290's forgiveness, and remove the two plastic ribs on the other half of the shaver (the side that doesn't cradle the motor). You can do this by working the plastic back and forth, gradually tearing off the two ribs all the way down to the shell of the body. If you don't do this, you will not be able to close the two halves together because this battery is larger than the original (the ribs cradled the smaller battery).
Solder the wires onto the correct tabs of the new battery (the tabs are not perforated, so solder the wires flat on the tabs), and carefully place it back into the body so that the wires run along the side, just like they did with the original battery. Now is a good time to find the little switch that gets triggered by the sliding button (the battery has a small charge to allow testing), so make sure the motor runs before you proceed. If not, check the connections and hope and pray that a wire did not break or come loose from a terminal on the switch or charger board at the base of the shaver. If all has gone well, position the two shaver halves, and push them together. They should snap into place. Charge the new battery using the shaver charger for at least 6 hours the first time. I hope it works as well for you...
***Update- as of September 2014, the battery is still holding a charge and performing well.