Update ??? : Abandoned Nicads and installed a 4-cell AA battery holder in the battery compartment. Use rechargeable AA eneloop brand batteries.
Update Oct. 2002: Bought a replacement set of Sub-C nicads at Radio Shack. They are different than my old ones. The Positive terminal of each cell sticks out far enough to avoid soldering wires between the cells. I only had to solder a wire to the Positive end of the 4th cell. :-) Because the new cells were shorter than the original set, I had to add a wood spacer at the positive end of the four. These batteries were poor quality. They did not last long.
The 2010 should have been designed to use 4 cells, not 3. Full use of the 2010 dies when batteries are HALF used up. This is VERY wasteful.
Install 4 Sub-C nicads in the battery compartment, and install a closed-circuit charge jack on the rear of the 2010.
You put a current-limiting resistor in the negative charge lead. You reroute the positive feed from the batteries to the radio, and wire it via the feed-through terminals of a closed-circuit jack. The jack interrupts feed-through voltage to the radio while charging, so that the higher charging-voltage does not get to the radio to harm it.
What you need to do is modify the 2010 to accept power from four sub-C sized ni-cads, rather than three "D" size ones. The additional cell provides the voltage that the radio needs, (4.8 v nominal vs. the 4.5 it normally asks for, and the 3.6 that three "D" ni-cads provide) and allows you to save some land-fill space. The catch is that sub-Cs are smaller in diameter than "D"s and will rattle around inside the case if you don't do something more than try to slip them into the radio's back.
To do this, wrap the smaller sub-C cells in electrical tape until they fit snugly inside one-inch automotive heater hose. Cut the heater hose into 4 lengths to fit the batteries. The heater hose's outside diameter is just the right size to simulate "D" batteries! (But check its diameter when you buy it.) [If necessary, put electrical tape over the positive ends of the batteries, leaving just the solder tabs sticking out. - May not be necessary; see "Update" above.]
Now comes the complicated part. Since this mod requires permanently attaching the batteries, you will need to add a jack to recharge the batteries "in-place". This is done by installing a closed-circuit jack (to match a 7.5 - 9 volt nominal power adapter) on the radio's back between the main board and the speaker, in such a way that it will hide behind the flip-up stand on the 2010. (If it won't fit under the flip- up stand, you might have to try drilling a larger clearance hole in the flip-up stand.) I used a sub-mini jack and changed the connector on the AC adapter I bought. Watch polarity!
Of course, before you do any of this, you need to remove the back of the radio and measure and drill carefully! The closed-circuit jack allows you to disconnect the batteries from the radio during recharging. Now with the back off, put some electrical tape over the positive terminal of the 2010 radio battery holder (you do not want it to short against the batteries!). Use a short piece of wire to connect two of the sub-C cells in series via the solder tabs, and then place them in the 2010 so that the end one presses against the big spring minus terminal. Add the next two cells to the 2010 one at a time with short wires. [You may be able to avoid soldering wires between the cells, see "Update" above.] Lastly, solder a length of wire to the positive end of the fourth cell long enough to reach the charge jack.
Now is time to figure out what value resister to use. Attach the adapter with a test resistor (watch the wattage!) in series with the batteries to get about 100-150 mA of charging current through the batteries. Try two 68-ohm 1/2-watt resistors in parallel. Once you determine the correct value, solder the resistor(s) to the common terminal of the jack and connect the other end to the battery holder negative terminal.
Next connect the wire from the positive end of the nicad array to the tip connector of the jack. Connect the 2010's positive battery terminal (now isolated from batteries) to the feed-through terminal of the jack.
For extra safety, try to switch the Main-Power switch off before charging. It shouldn't hurt the radio if you forget. That's why a closed circuit jack is used.
The down side -- this mod forces you to remove the back of the radio to change the computer (AA) batteries.
Larry Russell .... in Flushing, Michigan
Inspirational thanks to a technical article in NASWA or SPEEDX which described using 3 nicads, and charging them via the radio's built-in power jack. (An inadequate solution.)