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South Hills ARC
Username: Admin

Registered: 03-2006
Posted on Saturday, December 06, 2008 - 06:09 pm:   

Rebuilding Your Own Battery Packs

By Jim Mounts - KA3EBX

A few years back, I bought a used Yaesu FT-727 dual-band HT. The HT was in great shape, and the original FNB-4A battery packs still worked rather well. I really made out on the deal, since it also included a vox headset, wall charger, and rapid desk charger.

I really loved that desk charger. I could drop one of my spare packs into it, and in just an hour, it was fully charged. It wasn't long before I realized the aftermath of what my shiny new desk charger had done to my battery packs. To put it killed them! I should have used the wall charger. Sure, it would have taken 14 hours to charge a battery, but at least I would have extended their life

Well, to make a long story short, I browsed through several popular Ham Radio catalogs, and found that it would have cost around $60.00 to replace my FNB-4A battery pack. What made matters worse was that I needed two of them. Very depressed, I put my handheld up on the shelf, and there it remained for the next 3 years.

Later, a friend of mine told me about how he sent his battery packs to a lady in California who rebuilt them with nickel metal hydride cells. Having raised my curiosity, I asked him for her number. It was pretty late at night, when I jotted down the number, so the next day when I got to work, just for the heck of it, I did a
search for her company on the world wide web: The NiCad Lady,

Here I found all kind of information (including pricing) on all of the types of battery packs she rebuilds. She also sells just the inserts (internally assembled battery cells) which you can install yourself, if you feel brave enough.

I decided to repair the packs myself, so I called and ordered just the inserts. The inserts cost $40.00, so I ordered two of them. My old FNB-4A packs were rated at 12VDC @ 500 mAh. The new ones would be rated at 12VDC @1.0Ah, twice the capacity!

It took about 5 days for the inserts to arrive. They looked almost identical to the old ones. They were already pre-assembled. All I had to do was remove the old ones, and solder in the new ones. It's a pretty easy task but here's some tips you might find helpful if you decide to do it yourself.

Although this article pertains to Yaesu's FNB-4A battery packs, many of the following tips should also apply when rebuilding another brand of battery pack.

1. On the top of the FNB-4A battery pack, there is a decal which has been applied over the seam between both halves of the battery pack. Cut the decal with an exacto knife, right along the seam. Don't remove it! It shows which probe is positive (+) and negative (-).

2. Using a very small flat blade screwdriver, carefully pry apart the two halves of the battery case. It should only be tacked together in a few places with glue. Once the halves are apart, lay them side by side. Be careful not to move them around too much, so that you don't break the wire leads.

3. Using a slightly larger flat blade screwdriver, gently pry the battery pack from the case. You will find that they have been glued to one of the halves of the battery case. The glue is pliable, but take care not crack the case.

4. Once the batteries are loose, unsolder the red (positive) wire, and black (negative) wire from the old batteries. You'll notice that there is also a white wire attached. Unsolder this wire at the bottom of the case. This wire tells the rapid charger which battery it is, so that the charger will apply the correct voltage & current. Since we will no longer be using the rapid charger, we won't need this wire. FYI: The temperature sensor will shut off the charging voltage/current to the battery if it detects overheating in the cells.

5. Remove the old batteries, and install the new batteries, orienting them identically to the way the old ones were installed. Solder the red and black wires to the batteries. You'll notice I didn't attempt to glue the new batteries to the case. This is to make it easier to replace the batteries in the future. If you can find some packing material (plastic peanuts are great), and wedge pieces of the material between the sides of the batteries and the case. You might also
wish to lay a flat piece of material on top of the batteries before attaching the remaining side of the battery cover. Using some plastic model cement, apply a small amount of glue (not a lot,
we want to be able to take them apart in the future) along the groove of the case, where the two halves will mesh. Close both halves together, and wrap a rubber band around the case.

6. Plug the wall charger into the bottom of the battery pack. Using a voltmeter, place both leads on the top terminals of the battery (the ones which connect to the HT). You should see the battery voltage slowly rise toward +12VDC. Don't be surprised if it reaches around +14VDC. This is normal. Let the battery charge overnight, and by that time the glue will have cured. Unplug the charger, and slide the pack onto the HT. Using the BATT function, the LCD readout should indicate 12.5V. Remove the pack, and continue charging for the recommended time specified by the battery manufacturer.

Rebuilding your own battery packs is fun, easy & considerably less expensive than purchasing new ones or having them rebuilt for you. They should give you years of trouble-free service. I have received quite a number of emails from fellow hams who have rebuilt their battery packs using this procedure and who have told me they have been extremely pleased with the new performance. Should you have any further questions regarding this article, please feel free to contact me by email at Additional information is available on our club's web site, SHARC-NET, at

NOTE: A word of caution about charging nickel metal hydride batteries: It is strongly recommended that you use a slow method of charging, generally 10% of rated capacity of the cell (ie: a 1200mAh cell should have a charger output of 120mAh), unless you have a "conditioner charger system". Also, due to the increased capacity of the cells, you will have to charge your packs for a longer length of time.

To calculate the appropriate charge time for your battery, use the following equations:

Slow Charge: (cell capacity in mAh/Charger output in mAh) x1.4
Fast Charge: (cell capacity in mAh/Charger output in mAh) x1.5

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