REVIEW: Convert AA Batteries to C or D

These days it seems every kids toy available (and plenty of big kid toys) takes batteries of one sort or another. Rechargeable AA's make a great alternative to disposable alkaline batteries, but what do you do about C and D size batteries?

There are NiMH batteries built to the C and D sizes (as well as 9 volt), however they tend to be expensive and require a specialized charger. You need to be careful as well with capacity, the rechargeable C and D sizes are often times the same capacity as a AA battery. Surprisingly, the Energizer system of falls into this unglamorous category.

Instead, I recommend using adapters that allow your AA batteries to fit in the battery compartment of your C or D powered device.

How is this possible?

All three battery sizes produce 1.5 volts in their disposable form (rechargeable batteries come rated at 1.2 volts). The 'AA' size is smaller in both length and diameter, so an adapter just has to fill in the extra space to fit the electrical terminals.

These Soshine C-size and D-size battery adapters from dealextreme.com perform exactly that function, and for a good price.

The D size adapters allows the use of 2 AA batteries at a time. This doubles the available capacity allowing less frequent battery changes.

The negative terminal end is a hinged door with a snap tight latch.

The latch takes a good amount of effort to open. In fact, those with weak fingernails probably need to use a screwdriver to avoid winding up with a broken nail.

The hinge too seems to be quite strong. Sometimes with hinged plastic I fret continually that it will break, not so with these. Overall I've been very happy with the quality of these adapters.

I have been similarly happy with the C size adapters, although I have not used them nearly as much as the D's.

Instead of being hinged at the end like the D's, the C's are hinged along the length of the adapter. This hinge is of similar high quality as the D adapter. The latch is much easier to open, but still does a good job locking the case around the battery.

I heartily recommend either battery adapter as a great companion gadget for your rechargeable AA batteries. There are other brands out there and I've tried a few of them, but the combination of features, especially on the D size adapter is unmatched.

TIP: Use "Dead" AA Batteries in Wall Clocks

When your AA powered gadget runs out of power, do you toss the batteries without thinking?

Many times those batteries still have plenty of power, just not for the device they were removed from. Wall clocks that use a single AA battery can run off a "dead" battery for 6 months or more.

The time will depend on how much voltage the battery can still provide. Which in turn is dependent upon how sensitive the original device was to voltage. The lower the voltage the device accepts, the more run down the batteries will be, and the shorter the time they will power the clock.

Even though I use mostly rechargeable batteries, there are still several applications where good old alkalines make the most sense. As a result, I have a stockpile of half used AA's in an old peanut butter jar just waiting to be used up in a clock.

So give those AA's a second life. It'll mean a few more battery changes, but you'll get the full life out of your AA's.

TIP: No excuse not to use rechargeable batteries

Alkaline batteries, specifically the AA size, enable all sorts of electronic gadgets. Many modern gadgets, however, go through AA's so quickly that it quickly becomes costly to keep the devices powered up.

The original rechargeable batteries were NiCAD or nickel-cadmium chemistry. They worked, and still have their uses in battery packs for cordless telephones and portable power tools, but as AA's, they are a little limited in today's gadgets. The capacity of these older chemistry batteries just can't keep up with modern demands. in addition, they suffer from a detrimental memory effect which can lead to a permanent reduction in the battery's capacity.


NiMH batteries took care of the memory issues and represented a significant improvement in capacity as measured by the milliampere-hour (mAh) rating. Instead of the sub 1000 mAh ratings for Ni-Cad AA's, ratings in the mid-2000's are common place and go as high as 2900 mAh (please be careful of manufacturer's ratings, some have a tendency to let's just say, round up, this is especially true of cheap no-name batteries).

The NiMH chemistry is not perfect, however. The batteries suffer from significant self-discharge and while they are often claimed to have long lives, they do seem to fall short of the claims if used 'hard' (ie high current draw applications).

Today, there is a second generation of NiMH batteries referred to as "low discharge". As one might presume, this newer chemistry addresses the self-discharge issue that plagues the standard NiMH. Nothing is free in life, however, and at least for now these batteries are of lower capacity than the high end standard NiMH. Most of these newer batteries fall in the 2000-2100 mAh capacity range.

Unfortunately, the industry has not come up with a good marketing term to discriminate between regular and low discharge NiMH batteries. The most common method of separation is the use of the term "pre-charged" somewhere on the low discharge battery package. Because of the low discharge properties, manufacturers are able to ship the batteries already charged and ready to insert into your electronics.

So if you haven't already, give rechargeables a try, there's something for everyone! I recommend high capacity standard NiMH for high current draw applications to maximize battery life. For low current draw applications, the low discharge version is the best choice.

FAIL: Cordless Drill Battery Modification

Not every DIY project succeeds. Sometimes, there are failures. Sometimes the failures are pretty spectacular. It is ok to fail, however, so long as you learn something. This is why I am sharing these not so successful projects.

A few years ago the battery pack in my Ryobi 9.6 volt cordless drill died, I decided a replacement battery was just too expensive for the value of the drill. I had nothing to lose with the battery at that point, so after disassembling it, I determined that a bunch of NiMH AA cells could replace the existing Ni-Cad 'sub C' cells for the same voltage, but with 30-50% increased capacity (mAh).

Thomas Distributing carries tabbed NiMH cells. The tabs make it easier to solder cells together to form a battery pack. So I ordered up the right amount of cells and set to work.

Not having performed a lot of electrical tinkering at that point in my life, I foolishly used 22 gauge wire to connect the battery tabs together. It's what I had on hand, but sometimes you just have to buy the right material for the job. The battery pack went together pretty easily and it wasn't long before I had it charged up and ready to go.

Unfortunately, this is where the story goes down hill...For a project I was working on, I needed to drive four 6" screws into solid oak blocks. I got through about one and a half before the smoke started pouring out of the battery compartment. I quickly tore it apart and separated the batteries, my heart racing the entire time.

The high torque required to drive the screws into the hard oak (it nearly stalled the drill) drew so much current from the battery pack that the wires heated up to the point of melting the insulation and causing the pack to short out. Several of the batteries got so hot that they vented acid inside the enclosure.

Undaunted, I ordered more batteries and rebuilt the battery pack using heavier gauge wire.

Since I still needed to drive the remaining screws, I again used them as my test subjects. I got through the remaining screws just as the smoke started pouring out of the battery pack, again.

This time, before I could get it torn apart to stop the short, one of the cells exploded with a rather impressive bang!

That marked the end of my attempt at cordless drill battery pack re-building. I never figured out exactly what caused the second meltdown. Obviously something shorted out, but it didn't appear to be the same problem as before.

Under normal use the re-built battery pack would have worked just fine, but the extreme test conditions I put it through were too much. I would rather have an early failure, however, than to be lulled into a false sense of security. Especially considering the potential to have caused a fire.

So my recommendation is, don't try this at home. And by the way, I ended up spending more on the batteries than if I had just bought a new OEM battery pack.

REPAIR: Cordless Phone Battery Modification

My wife picked up a pair of cordless phones on Freecycle to replace our old phone that was dying a slow and staticy death. Unfortunately, one of the handsets didn't work when we plugged it in.


I suspected it was just a battery issue, and after swapping batteries between the two handsets was able to confirm my suspicion.

Since I had recently replaced the battery in the old phone, I figured no problem, just swap batteries. Or not, as it turns out the connectors between the two brands of phones are different.


There's nothing special about cordless phone batteries, in the end they are just 3 Ni-Cad AA's linked in series to give 3.6V at whatever capacity you want. The more milliamperes (mAh), the longer the talk time. In fact, you could easily buy your own batteries and wire them up to create your own battery pack. But, in this case I just wanted to swap connectors for a quick and dirty fix.

The swap is easy. Snip the wires on both batteries to remove the connectors. Strip a quarter inch or so of insulation from both the desired connector and new battery. The wires for both parts should be color coded red for positive and black for negative. Cross the stripped end of the red wires from the connector and battery and twist to create a connection.

If you feel motivated, the wires can be soldered together to guarantee the connection will not pull apart. I did not do this for two reasons. One, I was in a hurry to make sure the phone worked, and two, the soldered joint will be less flexible for installation in the phone. Another consideration is that the wires are not loaded once installed in the phone, so there is little to no risk of the splices being separated.

Now repeat for the black wires. When finished, wrap the wires individually in electrical tape to hold the splices together and prevent shorting. Re-install into the phone and you are done!

My phone has been operating on the modified battery for about a year now with no ill effects. In fact, we can't tell the difference between the two handsets unless the back cover is removed.

This method could easily be used to maximize the talk time for your cordless handset by utilizing a higher mAh battery pack than normal. You could also save a few bucks by picking the cheapest replacement battery available, regardless of brand and then adapting it to your phone.