Remove any batteries, then remove the screws from the case.  Please note that there is a potentiometer in what looks like a screw hole.  Don't mess with it.  

Once the case has been opened up, lay it on the table like in the picture above.

Connect a wire to the solder tabs as shown in the picture above.  Use whatever color wire you wish, but be sure to keep the polarity correct.  In this case, I used black for the negative connection, white for the positive.

Here's where I put my charging jack.  Make sure you don't drill the case until after it is taken apart, otherwise you might drill into something inside the radio.  The connector is out of the way of any of the internal parts, and is hidden on the back of the radio.  Connect the two wires from the battery tray that were soldered in the previous step.

Here's what the finished product looks like.  Looks as good as any factory jack, and is just as functional.

To charge the batteries, just connect it to the charger.  No more swapping batteries.

I chose NiMH batteries.  Nicad may be a better choice for you.  Let me explain.  NiMH have a higher internal resistance and will self-discharge in a matter of weeks.  So unless you charge the radio just prior to use, the pack may already be weak.  Nicads have a much better internal resistance and will maintain a charge longer when just sitting.

The big plus for NiMH batteries is their incredible capacity.  Just keep in mind everything has a price.  If you keep the pack charged, then NiMH would be a better choice.

Years ago I bought a couple of these chargers and Nicads to add to my Futaba radios.  They probably are no longer offered, but you can get a similar charger from places like Radio Shack.  Just get one rated at 9.6 Volts, and about 60 mA.  Just make sure that you buy a jack to fit your charger, or you'll need to change the plug to match.

When wiring your jack, make sure the polarity matches your charger!