Power to the people!
Most of today's hams carry their first ham shack in their pocket. The modern HT is a marvel of engineering, versatile, powerful, flexible, entertaining and useful, and having only one component that requires any thought-the battery. What exactly is inside that plastic case that snaps onto the radio and is sometimes larger than the radio itself? Only the culmination, in some cases, of over a hundred years of research and refinement, that wonderful device known as a rechargeable battery.
There are four basic types of battery used by hams today, with the Nicad and NiMh being far and away the most popular. The Nicad is a device steeped in folklore and surrounded by ceremony. It is praised and reviled. It is sworn by and sworn at in roughly equal measure, and its popularity is driven by one simple fact-it works very well for radio communication. The Nicad consists of nickel and cadmium electrodes separated by an electrochemical paste, usually spread thin and rolled up in a tube to maximize surface area. This construction helps give the Nicad the high power density and low internal resistance that make it so practical and useful as a portable rechargeable power source. It also helps explain why, if the battery is treated incorrectly, it will die so dead that nothing will revive it. Let's delve into the Nicad and peel back the mystery.
The sealed Nicad cell is an electrochemical system which converts, in a reversible way, chemical energy into electrical energy. To accomplish this the Nicad battery uses a nickel positive electrode with a cadmium negative electrode in a potassium hydroxide electrolyte.In a new Nicad, the crystals that from the barrier between electrode and electrolyte are small and distinct, and thus give maximum surface area for electrical storage. With use, or more particularly with

abuse, these crystals begin to from clumps that plate themselves with nickel, thus reducing surface area and storage potential. This is the dreaded "memory' effect that all Nicad users fear, which leads them to try to completely discharge the battery before recharging. Unfortunately, discharging the cell below the one volt level leads to the other big killer of the Nicad-cell reversal, in which the cell actually changes polarity . During the recharge cycle, this reversed cell heats up and causes outgassing of the electrolyte, further clumping of crystals and can even lead to crystals penetrating through the paste and touching both electrodes, causing internal shorts that drain the cell even while not being used. Given what perils can befall a Nicad, reaching the nominal expected life of 500 to 1000 charge/discharge cycles might seem an insurmountable task, but it is quite possible to get as many as 4000 cycles from an unabused Nicad. I replaced the nicads in an electric shaver with solder tabbed nicads from Radio Shack and got nine years of use from them, without using commercially available dischargers or any strange rituals. All that is required for happy nicads is to charge them when they need it. The discharge curve of a Nicad is such that it will deliver the rated power evenly over 80% to 90% of its discharge capacity, so when it seems low on charge, such as reduced transmit power or low voltage indication, charge it. Don't charge it for days at a time-an hour or so on fast charge if your charger supports it, or overnight for 12 to 16 hours on a normal charger will do nicely. Contrary to what the folks who are selling you "battery conditioners" will tell you, repeated deep discharges will damage your nicads. Repeated topping off charges will also damage your battery, by overcharging the cells and clumping your electrolyte. This is what leads to the memory effect-it's not that your battery is being trained to remember a certain level of charge, it is reducing the capacity of the battery through physical change. If you do by some chance induce memory into your batteries, which is actually a rare occurrence, then you will need to attempt several deep cycles and charge cycles in an attempt to break up the clumps and unplate the electrolyte. If a cell in your pack goes bad, chances are that the rest of the pack will fail soon, so it's much better to avoid problems by appropriate handling of that rather expensive battery pack. Proper charging involves monitoring the voltage of the cell while charging and tapering off the charging current as the cell reaches its maximum voltage

of 1.2 volts. Fast chargers also use a temperature sensing circuit to avoid cooking the cells during fast charging. The best way to charge a battery pack is to use a dedicated Nicad charger, either the one that usually comes with the radio or a charger engineered to work with nicads. Using a charger designed for LiIon or lead/acid batteries is begging for trouble.
Is it possible to buy individual Nicads to replace the dead cells in that expensive battery pack? Yes, it is, but the path to cell replacement is paved with certain caveats. The cells must be "matched" fairly closely in capacity, or you won't achieve the best performance, with the weak cell falling behind and causing the other cells to fail prematurely. Great care must be exercised in disassembling the battery, to avoid exposure to caustic battery paste and the possibility of burns from shorted cells. When shopping for replacement cells, make sure you buy the tabbed version instead of the regular button ends, as soldering to the button ends on conventional nicads will render the cell useless (don't ask me how I know this). It will take a few charge/recharge cycles until the battery reaches it full capacity, and during the initial break in period great care should be taken to not abuse the cell so it can "form" properly and give you the longest service life. Always use a sufficiently heavy wire gauge for internal battery connection-don't forget that you may be passing close to an ampere of current at six to nine volts to the radio during high power transmit, and the cells will be happy to give you enough current to set the battery on fire. And if you don't get the performance you were hoping for, don't panic-you may need to buy some more cells to try closer matching, and make sure those connections are correct. Like so many other endeavors, it's always worth a try.
Don't forget to properly dispose of the Nicad once it has finally expired, as the cadmium in the cell makes it a hazardous waste material that must, by law, be recycled or reclaimed properly. Never chuck the cell into a fire, as it can explode forcefully, and don't carry loose batteries or battery packs in your pocket or let them rattle around in you junk box-the nicads low internal resistance and high power