Rechargeable Batteries and Smart Chargers:

by Bruce Switalla and Patty Waits Beasley

We thought we’d better clarify our June CAUG meeting discussion on this topic in case there was any confusion. I’m STILL confused about “intelligent” battery chargers, so Patty will pick up that topic. Rechargeables are recommended for their long-term money-saving value.

Almost 30 years after the first nickel cadmium (NiCad) batteries powered video and still cameras (and cordless drills and flashlights for that matter), they are still the best-selling formulation for the pro-video market. This is according to the August 2002 Digital Video magazine, from which I’m getting much of this information. However, when we buy a consumer digital camera, we have little choice for the chemistry inside our batteries unless they come in the form of AAs or AAAs. As you know, you can get plain or alkaline disposables anywhere, and NiMH rechargeable AAs are available at a growing number of retailers. In the late 1990's, nickel-metal hydride, (NiMH) was a rechargeable formulation adopted by many manufacturers. And lately, lithium-ion (LiIon) batteries are gaining popularity.

Which one is right? Well, if you have a choice, NiCads have lots of energy, work well in cold weather, and have a long service life. But they are heavy and if you don’t drain their power completely before recharging, they can develop a “memory effect” after several times. This means they will only work half as long as originally. But there is hope. I learned from DV mag that you can actually condition these back by repeatedly fully discharging their power before charging again. But its better to not let this happen in the first place. This is best accomplished with an “intelligent” charger, explained later.

I thought I got a good charger that kept my batteries “trickle-charged” until I needed to use them. Then I read the July 23 “Digital Focus” Q&A and found out this warm trickle-charging is actually taking longevity out of my investment (rechargeables are expensive to buy). See this page,aid,102552,pg,3,00.asp

The cadmium in NiCads is toxic, but the NiMH formulation is more environmentally friendly. NiMH also has a better power-to-weight ratio, but they don’t do as well in cold weather. Nor do they have as long a life, accepting 300 charges according to DV magazine. The Dave Johnson article says they have a 500-charge life, but the Ray-O-Vac pkg. says they’re good for 1000. I have found that both NiCads and NiMHs will slowly self-discharge when left unused.

The LiIons are “joining the circus”, being used now in some of the more expensive cameras. But they actually require special circuitry to prevent overcharging and overdischarging. They appear to be the most expensive of the group and they will not work in my Energizer “not-so-intelligent” charger. Now we’ll shed more light on “smart” or “intelligent” chargers. 

Intelligent Chargers

The worst thing you can do is overcharge your batteries. But how do you know when that point’s been reached? The best way is to use what’s called a “smart charger” which is simply a recharger that has a microprocessor in it to monitor the amount of charge being administered. These smart chargers know just the right charge for the batteries they’ll accept. Depending on the design, the smart charger will either shut off the charging mechanism once the appopriate charge level is reached for that battery, or switch over to a trickle charge. 

Some chargers also have what’s known as conditioning circuitry. This is desirable, especially for NiCad batteries. As mentioned, NiCads have a tendency to adopt a “memory” of whatever charge level was administrated, whether it was for the battery’s full capacity, or to “top it off” if the battery was inserted with a partial charge still remaining. The conditioning charger will immediately drain off any surplus charge still in the battery, then proceed to charge the entire unit to its full capacity. These chargers will also monitor the status of charge being administrated, and will shut off or switch to trickle upon completion of the recharge. Trickle chargers keep the batteries fully charged without overtaxing the capacity. 

Avoid using chargers that just administer a set amount of charge time. Not only will it not be efficient for many battery designs, but it could actually overcharge and damage the battery. 

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