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Mobile phone batteries are way over the odds. You can buy this NEC Sportz phone for $299 with $1000 worth of free weekend calls but the battery will set you back anywhere up to $100 or so. The open battery in this photo has just had its cells replaced for $25! DEAD PHONE BATTERY? Don’t toss it – refill it with standard AA rechargeable cells Dead battery in your bat-phone again? Getting sick of paying out big dollars to replace it? Well cheer up. In this article, we show you how to replace the cells in your mobile phone batteries with standard AA-size nicad cells and save heaps of dollars. By ROSS TESTER 6  Silicon Chip If you’re one of the million plus Australians who owns a mobile phone, chances are you have already discovered one of the negative aspects: the price of replacement batteries. Sure, mobile phones themselves have dropped in price dramatically in recent years. The phone shown above, an NEC Sportz, is a classic example. When purchased two years ago it cost me the best part of a thousand dollars – $899 to be precise. Yesterday, I saw an advertisement for the same phone for just $299, with a thousand dollar’s worth of weekend calls thrown in for nothing! That’s progress, I guess. Fig.1: reproduced from the August 1994 issue, this Nicad Zapper circuit charg­es two 1000µF capacitors to 33V. This charge is then dumped through the dud cell by Mosfet Q7 when the ZAP button is pressed. It’s a pity that the same thing hasn’t happened to mobile phone batteries. Unfortunately, this is the one “expendable” where they can really get at you. Or at least they could until now. Typical replacement mobile phone batteries will set you back anywhere from about $50 up to more than $100. And that’s for the “ordinary” models which give you minimum talk time. If you want the “super” batteries which last a lot longer, be prepared to pay significantly more. In addition, buying genuine (ie, branded) phone batteries will set you back even more. The service life of mobile phone batteries leaves a lot to be desired, mainly due to the way we treat (or mistreat) them. Manufacturers normally rate their nicad cells for at least 1000 charge/discharge cycles but most mobile phone users find that their batteries last a year or less. Last time we checked, there were less that 1000 days in a year, so it follows we are doing something wrong! Nicad problems Many readers would be aware of the various problems which befall nickel cadmium batteries but to briefly recap, here are just some of them: (1) Memory effect – the battery loses capacity by being constant­ ly discharged only partially and then recharged. For example, you take your phone out for the day, then you come home and bung it on the charger so it’s ready for next day. The problem, of course, is that the battery is only par­tially discharged and never receives a full charge. Over time, it “remembers” this amount of charge, and this becomes its total capacity. Memory effect can be cured by a few cycles of complete discharge and recharge but you need to know when your batteries are discharged. Generally, if you wait until your phone starts beeping with its low battery signal you can be sure it is dis­charged but that brings us to another problem. (2) Reverse polarity cells – all phone batteries are composed of a number of individual cells connected in series. In a typical 6V phone battery, there will be five nicad cells, each rated at 1.2V (5 x 1.2 = 6V). However, not all nicad cells in a pack are born equal. Some may discharge further than others, and the charge/discharge patterns may actually cause one or more cells to be discharged “below zero” so that they become reverse polari­ty. This is a prime reason for battery failure. (3) Dendrites – the ideal battery would never lose its charge while waiting to be used. Unfortunately, this is not the case – all cells discharge over time. Also over time, crystalline growths may occur inside the cell which has the effect of in­ creasing the internal leakage current dramatically. These growths, called dendrites, will eventually short out a cell and are another major reason for battery failure. (4) Overcharging – all batteries have Fig.2: if you have a DC power supply which can deliver more than 30V, you can use this circuit to zap dud nicad cells. April 1996  7 The battery on the left, from an Ericsson GH198, was given a new lease of life by “zapping” bad cells. The battery on the right, from an NEC Sportz, was completely renewed. This photo shows the Ericsson and NEC batteries with their cases disassembled. The Ericsson was delightfully simple, the NEC took a little more work! a correct charge rate and a correct time to be charged. Exceed either of these, and you risk overcharging. Usually, this means a build-up of heat which will ultimately cause irreparable damage inside the cell. Often it will cause the cell to start leaking fluid and that leads to corrosion and general degradation. Occasionally, this heat build up is so dramatic that it blows the cell apart. Many phones have smart chargers which monitor the state of charge and adjust automatically. Many do not –they rely on the user to remove the battery once it is charged. And that doesn’t always happen! (5) Corrosion – surprising though it may seem, many users fail to recognise the need to keep battery contacts (both charging con­tacts and 8  Silicon Chip phone contacts) clean. This can lead to a battery not charging properly, or not being able to deliver power to the phone. Resurrecting a dead battery There are three steps to breathing new life into an appar­ently dead battery. The first is quite simple – clean the con­tacts on the battery, the phone and on the charger. For people living near the sea or in industrial areas, this is an all-too-common problem and one which many people seem blissfully unaware of. You might find that after cleaning the contacts, the battery accepts charge and works quite satisfactorily. The second is a little more complex, involving the opening of the battery case and checking the individual cells with a multimeter. You may well find that one, two or even most cells are quite OK, each measuring around 1.2V. However, it is quite likely that at least one cell and maybe a couple are showing either very low or no voltage. These cells need to be zapped or replaced. We have talked about zapping nicad cells in past issues of SILICON CHIP. If cells are low in charge due to den­drites, you can often fix them by zapping. This literally blows up the den­drites by applying a very brief but powerful charge to the cell. This technique was covered, along with a Nicad Zapper to build, in the August 1994 issue. This circuit is shown as Fig.1. Don’t be tempted to apply a high voltage directly from a power supply to the cell in the hope that this will blow the dendrites away. All you will succeed in doing is permanently cooking the cell and you might even damage your power supply in the process. However, if you have a suitable power supply, you can use the circuit of Fig.2 to make a cut-down version of a Nicad Zapper which is just as effective. We were able to fully restore an apparently dead phone battery to life using the Nicad Zapper. The technique is to “zap” individual cells, not the whole battery at once. To do this, the battery case must be opened and we will show you how to do this shortly. As luck would have it, the battery concerned (for an Erics­son phone) was one of the easier ones to disassemble. Once this was achieved, we had to zap one particularly difficult cell half a dozen times but eventually it said “I give up” and ac­cepted charge. In this battery, there was only one cell apparently dead, with only a couple of hundred millivolts across it instead of more than 1.1V for each of the rest. It was the obvious target for “zapping.” You don’t need to disconnect the cell to be zapped from the other cells. Instead, you simply connect the leads from the zapper across the cell concerned (taking care of polarity) and press the button. It’s easy to check whether your “zapping” has worked, simply by measuring the voltage across the suspect cell after the whole battery has been on charge for a few hours. Take the bat­tery off charge and measure each Corrosion is a major cause of rechargeable battery problems. These contacts clearly show a bad case of oxidisation – no wonder it wouldn’t charge properly. cell. Depending on how long they have been on the charger, they should all be somewhere between 1.1V and 1.2V (or maybe higher if they are almost fully charged). If the zapped cell looks OK, put the battery back on to fully charge it and then leave it for a day or so. This done, check all the cells again. If they are all close to the same voltage (ie, 1.2V), then you cured it. On the other hand, if the suspect cell has dropped to below 1V, you can assume it still has a few problems! Try zapping it again – you’ve got nothing to lose. You may cure it or if the cell is really dead, you’re not going to do any more damage by over-zapping it! Ultimately, nicads do wear out; the chemical components become exhausted and will no longer support the reaction neces­ sary to recharge a cell. Again, cell voltage is a good check of this. Cell strategy So what if you have one or more dead cells in your battery? Do you just replace dead cells or replace the lot? The answer is to replace the lot. This might seem like overkill but is the only practical approach. For a start, if you place one or two new cells into a bat­tery, the new cells will almost certainly have more capacity than the old cells, even if their label ratings are identical. It stands to reason that a brand new cell will always have more capacity than an old cell. If you have cells of different ages in a battery, its capacity will always be limited to that of the weakest cell in the pack – it’s like the weakest link in the chain. So if you put one or two new cells in a battery, you will be wasting your money. Do the job properly and fit all new cells – you will still be saving heaps of money over the cost of a new sealed battery! Just as importantly, instead of the measly 700mAh battery which came with your phone, you will end up with at least a 1000mAh battery, which will give you hours more standby and talk time! YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM Nicads or NiMH? SATELLITE ENTHUSIASTS STARTER KIT Throughout this feature, we have talked about nickel cadmi­um (nicad) batteries as if they were the only types used. One of the more recent batteries to come onto the consumer market is the nickel metal hydride, or NiMH, type. These offer some advantages over nicads. For a start, NiMH batteries do not develop a memory. They are much more forgiving of the type of charge/ discharge cycles we consumers inflict on them, and they are much more environmen­tally friendly in manufacture and disposal. Most importantly, size for size NiMH batteries offer sig­ nificantly better capacity than their nicad counterparts. For example, the AA types we feature in this article offer a 1000mAh capacity in nicad form and 1100mAh capacity in NiMH form. On the downside, they are more expensive and they are not suitable for high discharge applications such as in battery-powered tools and radiocontrolled toys. There is also the question of whether chargers, especially smart chargers, designed for nicads would be suitable for NiMH batteries. It’s a question that we have not been able to get firm answers for. Experience, though, suggests that every charger we have tried has no problem whatsoever with NiMH batteries. We have used both types in preparing a number of batteries for this article. All original batteries were nicads, as would be expected, but when replaced all have performed at least as well as the original (and usually much better), whether fitted with nicads or NiMH cells. Note that which ever cell you choose, make sure it has solder tags. It is possible to solder to cells but it is not easy and when they are available with solder tags already on, why not take advantage of them? You place YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 April 1996  9 This photo shows how to open up the battery. If it is gripped along an edge as shown and the vise slowly tightened, eventually the weld or glue will give. Suitable tools (eg, a table knife) can then be used to open up the crack. To fully open the case, continue working slowly around the edge with the knife. The screwdriver prevents the case from closing again. the cells under much less stress by soldering to tags. Opening the case The manufacturers don’t want you to replace cells. They want you to buy a new battery! Because of this, they don’t make it easy to open up the case, usually welding it or seamlessly gluing it. But if you know the secret, it’s not too hard to defeat this. The technique for opening any welded plastic battery case is to apply 10  Silicon Chip just enough pressure in the right place to make it give. This is most easily achieved in a bench vise, because the pressure is very easily controlled. Sometimes, it is not even necessary to go to this level. The battery for the Ericsson, for example, came apart very easily once we removed the label covering the back of the battery. Examine the case carefully – it should be possible to make a reasonable guess as to where the halves of the case join. Place the battery so that this seam runs lengthwise from one jaw to the other in the vise (as shown in the accompanying photo). The battery should be positioned so that it is just gripped along the very edge to be broken. Now very slowly tighten the vise so that pressure is ap­plied to the seam. If all goes well, before too long you should hear a reassuring “crack” as the first seam gives way. Sometimes, I have found it necessary to give a little extra help by tapping lightly along the seam with a small hammer, or even a knife handle. Eventually, you should hear that “crack” and you’re on your way. Don’t be too concerned if the seam doesn’t break completely cleanly – after all, you are breaking a weld. Besides, it will be glued together later anyway. It is also possible that the plastic may crack in the wrong place –again, a dab of super glue later will generally fix this up. The best tool for expanding the seam is an ordinary table knife. It doesn’t need to be sharp (in fact, it’s safer if it’s blunt) – just as long as it’s thin enough to work into the seam, and wide enough to give a little leverage. Use a second knife or a thin blade screwdriver to keep working your way around the seam until you have lifted it on all four sides. Before opening up the battery completely, prise it apart slightly and see how the cells are assembled inside. You might find that they have used some glue, double sided tape, wax or other gunk to hold the batteries together or in place. Just take your time, prising the case apart slowly until you’re sure you can see what goes where. Inside the case, you’re likely to find a polarity protection diode, perhaps a thermistor or some other components. Make a note (or drawing) of how and where these are placed and connected. Incidentally, we did find one slightly disturbing thing when breaking apart several batteries for the NEC Sportz phone. The genuine NEC battery contained protection components, while the significantly cheaper non-genuine “equivalent” replaced these with lengths of wire! Once you have the case apart, you might have to carefully remove some insulation to gain access to the individual cells. At this point, you can decide wheth- the replacement cells, keep your solder joints as thin as possible. We found that tucking a negative-end tag under the positive-end tag achieved the minimum bulk. You might find that some solder tags need to be trimmed a little shorter if space is very tight in your battery but so far we haven’t had to do that. You might also find it necessary, as we did in one battery, to solder the tags at approximately 15° angles to each other in order to get the cells to fit. Experiment with your cells before soldering. If using the connecting straps from the original cells leave them until last. Double and triple check your positive and negative terminals before soldering the straps into place. Reassembly This battery is from the surf club transceiver pictured on the next page. Unlike mobile phone batteries, this is rated at 7.2V and therefore required six new cells. As you can see, there is plenty of room inside the case. er you want to persevere and “zap” cells, or simply replace the lot. In many ways, the second option is the best, because you know you have a brand new battery when it’s done. It’s obviously the only route to follow if you don’t have a zapper. Removing cells In all batteries that we have disassembled, the cells themselves are welded together. This is a pity, because if at all possible, we want to use the same connecting straps on the new cells. These were made to fit the case. The straps are usually spot-welded to the first and last cell in the string but they usually come free with a little coaxing (ie, with pliers). In the case of the NEC Sportz battery, the connecting straps also form the connection to the charging contacts as well as the phone power contacts, so it was imperative to get the straps off in one piece. Other batteries have separate contacts moulded onto the case and are connected by flying leads. Remember if soldering or unsoldering to a moulded contact, apply heat for as short a time as possible. Any insulation or other material removed should be kept as intact as possible for reuse. In some cases, due to the method of original manufacture, this may be impossible. However, keep any broken pieces to make fabrication of new pieces easier. Replacing cells The major difference between original cells and replacement cells is that, in most cases, the original cells don’t have a raised “dimple” on top which marks the positive end; they may not even have positive or negative markings on them, so be careful when identifying which end is which! That dimple on the replacement cells could create a space problem but so far we haven’t found any cases that can’t accommodate the slightly longer replacement cells. Because the cells are connected in series, it’s simply a matter of soldering positive to negative in the right position – use the cells which came out as a guide. It’s always wise to pre-tin the solder tags and, contrary to what you might imagine, a good, hot iron is better than a lukewarm one. It gets the job done quicker, before the battery has a chance to think “Hey, I’m getting hot!”. Check and double check your solder connections. Keeping in mind our comments about the extra length of Refit any protection diodes, therm­ istors, etc, to exactly the same positions and cells as they were originally. Your charg­er might rely on certain connections to sense charge levels and cell temperature to avoid overcharging. Be sure also to replace any insulation (preferably the original insulation). In many batteries we have seen, the con­ necting straps are separated from the battery terminals by a thin piece of insulation – if this is creased or bent out of shape, shorts are almost inevitable. We have found that in some cases the replacement cells are smaller in diameter than the original cells. In this case, it may be necessary to provide a small amount of packing (eg, cardboard) inside the case to prevent cell movement. Naturally, any packing material that was used in the origi­nal cells should be re-packed if possible. Where cells are a tight fit, we found the kitchen knife a handy tool to help slightly expand the case as cells were re-inserted. If possible, you should do a “dummy run” of the new battery before final assembly. With it held together as far as possible, check with a multimeter that voltage appears at the phone termi­ nals. Check that the charging contacts make contact with the charger (most chargers have some form of indication) and that the battery still clips on to the phone. If all appears well, reassemble the case with a tiny drop of super glue at April 1996  11 each of the four corners. Ensure that the case is clamped together for five minutes or so, until the glue dries. You don’t want to use more glue that necessary – after all, in a year or so, you might want to replace the cells again! It will be so much easier the next time around because you will know exactly what to do. Transceiver batteries We mentioned before that mobile phone batteries aren’t the only ones which can be refurbished. In fact, The techniques are not limited to mobile phone batteries. This UHF transceiver belongs to a surf life saving club and their batteries are even more expensive. Six new NiMH cells and an hour’s work saved them more than $80 for a new battery! while this article was in preparation we received a call from the local Narrabeen Beach Surf Life Saving Club. They had just been told that the batteries for their hand-held UHF radio transceivers had gone up to more than $100 plus tax (or more than $130). As volunteers, their finances were already stretched beyond the limit. Using the techniques described in this article, we cracked open two of their defunct batteries and replaced the cells – one with NiMH cells and the other with nicads. Probably the only real difference between these batteries and mobile phone batteries was that they took six cells (7.2V) and there was still plenty of room inside the cases. The chargers used by the Surf Club are very sophisticated models, offering a switched choice of standard trickle charge or a 1-hour rapid charge with au­tomatic switch-over to trickle charge. Without wanting to delve too much into the charger elec­tronics, we want­ ed to know if there was any difference between the NiMH and the nicad batteries. As far as we can tell, both new batteries behave identically. Charging times appeared similar, switch over to trickle charge is identical and radio operation is the same except for the slightly longer operation of the NiMH battery. What about other transceivers, such as handheld units for the CB or amateur bands? As far as we can tell, the process described here still applies and you can save heaps of money. Special offer from Jaycar High capacity rechargeable cells are not normally all that easy to buy, especially at a reasonable price, but Jaycar Elec­tronics has made a huge purchase of them and is offering them at very good prices. For example, 1000mAh AA nicad batteries, with solder tags, are just $5 each and 1100mAh AA NiMH batteries, also with solder tags, are just $6.25 each. But exclusively for SILICON CHIP readers, Jaycar has agreed to a bargain offer: buy four cells and get the fifth one free! And for the vast majority of readers wishing to refurbish phone batteries, five cells just happens to be exactly what they need. So for AA nicads, you pay just $20.00 for five (instead of $25) and for AA NiMH cells you pay $25 (instead of $31.25). To take advantage of the offer, fill in the coupon below (or a photocopy) and take it with you to your near­est Jaycar Electronics store (offer also available through Jaycar mail order). Note: this offer is available for two months only, until 31st May 1996. References For additional reading on the care of nicad batteries, these articles will be of use: (1). An Automatic Nicad Battery Discharger; SILICON CHIP, Novem­ber 1992. (2) Single Nicad Cell Discharger; SILICON CHIP, May 1993. (3) Nicad Zapper; SILICON CHIP, August 1994. (4) Automatic Discharger For Nicad Battery Packs; SILICON CHIP, September 1994. (5) A Fast Charger For Nicad Batteries; SILICON CHIP, October 1995. (6) Reflex (“Burp”) Charging Nicad Batteries For Long Life; SILICON CHIP, SC January 1996. Jaycar Nicad/NiMH AA Battery Offer For the months of April & May 1996 only, Jaycar Electronics is making the following special offer to SILICON CHIP readers: buy four AA 1000mAh nicad cells with solder tags (Cat. SB-2441) or four AA 1100mAh NiMH cells with solder tags (Cat. SB-2457) and get a 5th cell for free. That's represents a saving of $5 for the nicad cells and $6.25 for the NiMH cells. You can take advantage of this offer only by filling in this coupon and taking it to your nearest Jaycar store; or fax or mail the coupon to Jaycar’s mail order department. Yes! please supply: ❏ 5 1000mAh nicad cells ($20)   ❏ 5 1100mAh NiMH cells ($25) Name ___________________________________________ Street ___________________________________________ Suburb/town_______________________ Postcode _______ 12  Silicon Chip Note: please include credit card details for mail order & add $4 for p&p. Offer expires 31st May, 1996.