Buying rechargeable AA, C and D cells for your Walkman (TM), flashlight, GPS, toys, etc. can be a very good investment. If you factor the cost of disposable alkaline batteries over the service life of rechargeables, the cost for disposables is almost 1000 times higher! Add to this the factor of pollution in landfills from disposables, and the choice of using rechargeables is a very good one. However, rechargeable NiCad and NiMH cells are not suited for every application. Hopefully, our advice will be helpful for your choices.
Disposable Alkaline Cells--These are very powerful batteries and will work for all applications. However, they are incredibly expensive to just use and throw away. Don't even bother with chargers that say they will recharge disposable cells...the batteries are not designed for this, and you will be wasting your money if you have to depend on the batteries like we do up in the mountains. Advantages--long storage life without use, very powerful, available everywhere, just use and throw away. Disadvantages--Very expensive since they can only be used once, heavy, pollution concerns in landfills, poor power output in cold temperatures.
Use disposable alkalines when your electronic equipment must sit for months without use. An example would be the flashlight in your drawer or truck that hardly ever gets used. Our radios in the local volunteer fire department have all been converted over to use disposable alkaline cells for this reason (at a cost of $50 per radio--they were designed for NiCads). Rechargeables self discharge very fast compared to disposables, and our radios must be ultra-reliable, since hazards to life and limb are involved. A few incidents where NiCad powered radios were dead after sitting for 3 months in the fire truck was all that it took to convince us. The alkaline cells perform admirably in these conditions, and we haven't had a problem since the conversion. Of course, the cost of these disposable cells comes out of the fire department budget and not our pockets.
NiCad (Nickel Cadmium) Rechargeable Cells--These can be found almost everywhere, from laptop computers to cordless phones to electric shavers. However, they are being quickly phased out in favor of NiMH (Nickel Metal Hydride) cells because Cadmium is a VERY toxic metal that lasts forever in landfills and pollutes groundwater...even rechargeables eventually end up in landfills. Don't be guilty of this! Most battery dealers will accept dead NiCad cells for recycling! Though the initial cost is high for the batteries and charger, they save a substantial amount of money in the long run. These cells self-discharge quickly, and should not be used in applications where the device they power has to sit unused for months at a time. Advantages--can be recharged many times, good power compared to weight, constant voltage output until cell is discharged (flashlights don't gradually get dimmer and dimmer...they stay at the same brightness until they suddenly go out). Disadvantages--Toxic waste in landfills, fast self-discharge when sitting unused, regular chargers may actually damage batteries and reduce life, lower voltage (1.2 volts instead of 1.5 with disposables) means special adaptors are required in some equipment (though equipment designed for rechargeables may need an adaptor to use disposable batteries), very sensitive to overcharging or deep discharging.
The so-called "memory effect" in NiCads gets lots of press, and lots of special chargers designed to "fix" it. This is mostly a myth! NiCad cells can exhibit this effect in appliances like a "dustbuster" vacuum cleaner, where the appliance is used for only a couple minutes at a time and then put back on the charger. After a few months of this, the batteries will only charge up to the level they were discharged to over and over. In most applications, the memory effect is not even an issue, though special equipment is available that fully discharges ("conditions") the batteries before recharging. This is another myth! These batteries are ruined by being run down until they are empty, too, just like expensive remote power batteries. To avoid the dreaded "memory effect," every couple of months simply run your dustbuster or cordless drill longer than you need, until the motor -just- starts to slow down. Recharge it. Problem solved.
For best NiCad life, use your video camera or laptop until the batteries are ALMOST dead, but not completely. Avoid any product that claims to "condition" your batteries.
Recharge the batteries until they are full (use the time estimate that came with the equipment manual), then immediately remove them from the charger. NiCads are VERY sensitive to overcharging, and will be ruined in a few months if you let them sit in the charger.
If you are really anal-retentive about your batteries (a good thing--you'll save lots of money in replacements!), find a charger that charges first at a high rate (1 amp or so) with PWM (pulse-width modulation), then switches to a trickle charge to finish, then completely shuts off. We don't know of one that does this so far, please let us know if you have one. Plans are available in a back issue of Home Power magazine--we are currently experimenting with them.
NiMH (Nickel Metal Hydride) cells--These are the new high-tech replacement for NiCads. Most new laptop computers and cordless phones come equipped with these cells now. The biggest advantage is that dead batteries don't contain nearly as much toxic waste as NiCads, a good reason for switching in itself. Otherwise, their performance is similar to NiCads with a few real advantages besides. Advantages--Higher power density than NiCads (more power by size and weight), no toxic waste in the landfill, can be recharged many more times than NiCads, no "memory effect" (see above). Disadvantages--Even more sensitive to overcharging and complete discharging than NiCads, self discharge rate very high, so don't leave them sitting for even a couple weeks.
Within a few years, these cells will completely replace NiCads just by virtue of the toxic waste issue. Just keep in mind that if you leave NiMH cells sitting in the charger cradle for too long, you WILL ruin them.
Lithium Cells--While not rechargeable, these batteries have some special properties that make them very useful in certain applications. They have an incredible storage life--years and years without self-discharging. They pack more power than a standard alkaline cell, but weigh very little, and function perfectly in cold weather where alkalines would give up quickly. Use these very expensive, non-rechargeable for special applications. I use them for my firefighting equipment--flashlights, GPS, emergency strobes--where the equipment may sit for 2-3 months between uses.
Lithium Ion Cells--These are what's being used in many electric vehicles these days, and also in your laptop, smartphone etc. Too expensive for any off-grod power system -- so far. Stay tuned, another article coming soon.
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