Thursday, July 7, 2011

I have an HTX-202 hand-held transceiver. I would like to rebuild the battery pack ...

Q Paul, W5PDA, asks “I have an HTX-202 hand-held transceiver. I would like to rebuild the battery pack, but
I’m not sure how to go about doing it. Can you give me some

A Speaking as one who has rebuilt several battery packs (mostly for laptops), I have to caution against attempting it unless you have no other option. (Keep in mind that replacement packs are available from several aftermarket manufacturers. See the ads in this issue of QST.) If you choose to go ahead, proceed with caution.

The pack was assembled in such a way as to prevent disassembly. In order to disassemble it, you have to break it—there’s just no way around this. However, if you are very careful, you can break it in such a way that reassembling the pack is still possible, and with a reasonable appearance to boot. Start by studying the pack carefully. Try to figure out what holds it together. Come up with an idea of how to take it apart, then try to come up with reasons why that won’t work very well. When you have an idea with the least “won’t work” reasons, that’s the one you should use. 

Once you have the case apart, the rest is fairly easy. You will find multiple NiCd cells connected together with thin metal strips, usually spot-welded to the cells. Your next task is to find cells of the same size (typically nonstandard, but usually obtainable—try Digi-Key for one source). There is a caveat here: the original cells were probably matched according to their charge and discharge characteristics. If you buy unmatched cells, you won’t get as much use from a rebuilt pack because you’ll have the “weakest link in the chain” effect. 

Once you have the replacement cells in hand, you have to connect them together in some fashion. You can do this with wire and solder, or you can use the original strips if you can yank them off the old packs without cutting yourself (been there...).

To solder the wire or strips to the new batteries is a difficult
task because solder doesn’t like to stick to stainless steel or shiny aluminum (which is what most new batteries use as contact plates). First, warm up your soldering iron to its maximum temperature (if you have a 300-W iron, use it, although 60 W will do). Sandpaper or file the contacts on the new batteries to rough them up a bit so that the solder has a place to stick. Take your iron and heat the contact plate up as quickly as possible— a 3-second or longer “dwell” time will probably damage the battery, so keep it shorter than that. Apply solder to the contact to make sure it sticks. Once you get the solder to stick to the contact, add your wire/metal strip and “reflow” the solder.

Of course, when you do this, you also have to make sure that: (1) the new cells go together with the exact alignment of the old cells and (2) that the solder you added doesn’t cause the resulting pack to be too big to fit back in the old case.

Assuming you are able to connect all of the cells in a way that allows them to fit in the battery pack case, you’ll have to find a way to get the pack back together (glue, small screws, etc).

If this sounds like a lot of work, that’s because it is, but it is the cheapest way to get close to your original pack capacity. There is a much cheaper and easier alternative, but the price is in time per charge. Buy a battery case for the rig (made for alkalines) and just put NiCds in it. The capacity (and possibly the voltage) will be less than your original pack, but it is definitely a cheap and sweat-free alternative.

From QST April 2001