Care and Feeding of Rechargeables

Modern consumer electronic equipment uses two basic kinds of rechargeable cells. In order to care for them properly, we need to know what kind they are, because they require entirely different treatment when it comes to charging and discharging. They are Nickel Metal Hydride (NiMH) and Lithium Ion (Li-ion). A third kind, Lithium Polymer, has the same general characteristics as Li-ion, and we’ll refer to them all that way.

NOTE: There is another type of lithium cell, made by Eveready (Energizer e2 Lithium) and some other companies, that IS NOT RECHARGEABLE. These are the two-for-ten-buck jobs that are sold for cameras and small flash units. This information does not apply to them. They will explode if you attempt to recharge them! Always be sure the labels of any cells or batteries read “Rechargeable” unless you plan to discard them after one use.
NiMH cells are the removable D, C, AA and AAA cells that you buy at the camera shop or drugstore (or, if you’re smart, online) for use in cameras, flashlights, toys and similar applications. Properly cared for they will last a long time — hundreds of charge/discharge cycles. That’s if they’re properly cared for. NiMH cells are subject to a phenomenon known as memory imprinting that can greatly reduce their useful life if not dealt with properly. Let’s say you have a set, run them ¼ of the way down, and then recharge them. You continue to repeat this process because it’s easier to recharge them every night while you’re asleep, or whatever. After a while, due to memory imprinting, they will lose the capacity to hold a full charge, and will only hold ¼ (or less), the way you trained them to.

The newer NiMH cells can be recovered by treating them the way you should have to begin with, as explained below, but this kind of treatment will greatly shorten their useful life. Ideally these cells should be completely charged before use, and then completely discharged on every cycle. This can be done by running them down in the appliance in which they are being used, or with special chargers that “condition” them by first discharging them completely and then recharging them to full capacity. Cells treated in this manner will give good service for many hundreds of cycles. The more often they are partially charged/discharged, the shorter their total life will be. If your cells have already developed a memory, a couple of complete charge/discharge cycles should put them right again.

Obviously, this means you need at least two sets of NiMH cells, so that you won’t run out of electrons in the middle of something. Discharge set A completely, replace them with set B, and recharge A. Continue to use B until they are discharged, and so forth. This will not only increase the life of the individual cells, it will give you extra power when you need it on the road. (I use three sets.)

Now, PAY ATTENTION. The dedicated batteries that fit in your laptop, your new Razr, iPod, and similar appliances — the ones that are specially shaped to fit in only that appliance — are almost certainly Lithium Ion or Lithium Polymer. Look at the label on the battery. If they are either of those types, they need to be treated the exact opposite of NiMH.

Lithium-based rechargeables like frequent recharging. They are very happy being plugged into the car charger, carried around for a few hours, and plugged back in when you get home. They should be completely discharged only when absolutely necessary. They are not subject to memory imprinting, and perform best when charged frequently and completely. The exception to this is the first time the battery is used. They should be fully charged the first time, then discharged completely — one time. After that, charge early and often.

There is one other critical thing that you need to know: all rechargeables, especially lithium, hate heat. Do not leave your phone, iPod, or spare batteries in the car. They do not like being stored at high temperatures for even short periods of time. Use only chargers intended for those batteries, even if others will fit. Chargers for Li-ions are designed to prevent the cells from overheating. Without that protection, there is danger of explosion and fire. Never use a charger other than one designed for your specific appliance. If you need to store a spare Li-ion battery, charge or discharge it to about the 40% level, then seal it in a plastic zipper bag and store it in the refrigerator. Don’t freeze it, just keep it in the door or someplace cold. Freezing it will damage the battery. Don’t store Li-ions fully charged or completely discharged.

A word about third party (bootleg) batteries. If you want to cheat yourself buying NiMH, OK, but you should never buy the cheap replacement Li-ion batteries and chargers that are sold in service stations, truck stops, and on some websites. Here’s why. Li-ion batteries are prevented from overheating by their “smart” chargers, backed up in case of failure by a smart circuit in the battery itself that cuts the current off and prevents overheating. The cheap chargers often dispense with the protective “smart” circuits, depending on the circuit in the battery to do the job. If it fails (more likely in the cheap bootlegs), you will likely experience a “failure with flame emission.” Replacement batteries from the manufacturer are expensive for a reason. It costs to build them properly. It’s no place to be cheap.

In the case of laptops, the battery should be removed if you are using the computer on the a/c adapter for long periods. Although they are designed not to overheat when charging, the batteries will remain at very high temperatures if left in the laptop because of the high operating temperatures inside the computer. Not only will they overheat and their lives be seriously shortened if constantly treated that way, they will cause higher temps inside the computer case that will eventually work mischief with the other electronics. In extreme cases, as we have seen with the recent Sony recalls, they can burst into flame.
The number one cause of computer battery failure is overheating in this fashion. It’s a bit of a pain to remove and replace the computer battery, but you will be rewarded with longer life from both it and the computer itself. Let it charge fully, then remove it if the laptop is to be used on fixed power. It’s OK to leave it on charge if the computer isn’t being used extensively.

Li-ion batteries in laptops should be fully discharged in the computer about every ten charging cycles. This is not necessary for the battery, but is needed to re-calibrate the fuel gauge, which will become progressively more optimistic if not cycled occasionally.

Remember, charge Li-ion cells the way they vote in Chicago: early and often.

You can learn a while lot more about batteries (if you want to) at Battery University.

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