Why should you get this charger instead of some other charger?
5 words: CHARGE, DISCHARGE, TEST, REFRESH and LCD!
CHARGE
Choose the individual charging rate for each battery, (200/500/700/1000/1500*/1800*mA).
Why choose the charging rate?
If you're rushing, charge fast and hot. If you're charging overnight or over dinner, charge more slowly. Slow charging is almost always gentler on the batteries, giving you a longer useful life.
Why set the charging rate individually?
You want this ability in case you have batteries of different capacities, partially discharged batteries, mixed brand/quality or any number of other reasons.
* Note
1500/1800mAh only available in Charge mode and only when charging 1 or 2 batteries in terminals 1 and/or 4.
DISCHARGE
This mode discharges the battery down to 1 volt then recharges to full capacity using Delta V measurement, at a user-selectable charging level*, of course.
Why discharge then charge?
This is the older technique developed to avoid capacity-robbing memory effect encountered when recharging NiCad-based batteries (which by the way are compatible with this charger, unlike the Maha mentioned below).
Why Delta V?
This is the modern measurement adopted by most "fast/rapid" chargers. While not quite as accurate as simultaneously using Temperature measurement and/or detecting Zero Delta V, as the Maha/PowerEx C-204W can do, it should be enough to prevent battery damage and insure complete, consistent charging.
* Note
Discharge rates are 1/2 the selected charging rate (max 1000mAh charging in this and other modes). Some batteries can take discharge rates this high, others can't. Most electronics don't drain batteries this fast continuously, so most batteries won't be any "healthier" if discharged too fast. Since this mode will probably take several hours to complete, do it overnight at the gentler 200mAh or 500mAh charging modes (and corresponding 100mAh/250mAh discharge modes).
TEST
Did you think that those little power strips on alkaline batteries were a good idea? I did, who doesn't want to know how much juice is left in a battery. The problem is the indicator bars weren't very meaningful and couldn't measure voltage too accurately.
Now, this charger can tell you more accurately the voltage output of your batteries (which you may interpret as an indication if it's fully charged > 1.40V or discharged < 1.20V). Still, that's just an indication of charged capacity. Why not a direct measurement?
The Test mode does just that. It measures the capacity of each battery and reports it. It initially charges each battery, discharges it (simultaneously measuring the mAh) and then recharges it, leaving you with full batteries and a record of how much juice it discharged during the test.
Why Test?
You ever pull open a drawer, find a rechargeable, wonder if it's "still any good," recharge it and then use it just to find out? This baby will do it all for you, giving you the answer for each battery as it finishes.
Another good reason is to verify the capacity of newly bought batteries. I'm using it now to check each battery in a brand 24-pack of Lenmar 2000s. It's found some clunkers which I'm saving for the next mode, which is...
REFRESH
If you're thinking this mode refreshes batteries, you're right. I haven't had the chance to use it yet, but you know I will. I've got some great candidates too, brand new clunkers from Lenmar, some good old "state of the art 1400mAh" Sanyo and Nexcell NiMH's and even some older NiCads (it may be cheaper in the short term to return them to service than to dispose of them).
You can't use this charger on alkalines or rechargeable alkalines, so don't even think about "refreshing" those in this charger.
One thing about the Refresh mode. Refreshing NiCads manually may take several cycles of charging and discharging. Not only does this charger perform the charge/discharge cycle as many as 20 times, it measures the capacity of each discharge cycle and stops refreshing when the capacity of each battery isn't improving anymore. With other chargers, you're probably overcharging some of the batteries just to get the others back up to snuff.
LCD
One thing the Maha doesn't have is an LCD readout (though their C-777 model does, maybe next year?). The BC-900 has an individual LCD readout for each battery, which you can set to alternatively display any of 4 different measurements (hours, volts, mA charge/discharge, mAh), in addition to continuous displaying the particular mode each battery is in. The LCD readout retains it's reading (e.g. tested mAh) until the battery is pulled out, making overnight "tests" possible. The LCD makes all the other charger modes informative and practical.
Shame on those other chargers that have LCD indicator bars but no numerical display (some even cost more than the BC-900).
Understand, as great as all the different modes and options of this charger are, without an informative LCD display, they would be "shot's in the dark". With the individual displays, I'm happily recharging batteries, checking the quality of each, refreshing some while storing the "truly" fully charged ones.
With the LCD, I'm getting an idea of just how good a pack of batteries (and hence brand) is.
ROOM FOR IMPROVEMENT
Transformer
The current power brick is oriented so that it may block adjacent outlets, so put it on the end of a powerstrip or AVR/UPS unit. My Nokia phone charger has the plugs on the edge so it's really low profile on the outlet.
While the transformer is thankfully a bit slimmer than most external units, it is also a bit longer than most (about 1.75in by 3). It is however Autovolt from 100-240V, although another reviewer mentioned the 3V DC output was sort of a pain.
I wish this charger had a built-in power transformer and a retractable cord.
Cooling fan
Batteries get hot from charging, they'll read hot too. A built-in cooling fan would keep the batteries cooler during charging and probably give a more accurate "just-charged" reading on the LCDs. Some other high end chargers have fans built-in, so I'd hate to see this "ultimate" charger get upstaged by lacking such a common-sense $1 feature.
Free Bag
The unit comes with a free bag which is much roomier than necessary. I could fit my Casio Exilim camera, dock & transformer for the Casio, backup compact film camera along with the battery charger, C/D-cell adapters and 24-pack of batteries in the bag. While I feel sort of silly mentioning a quirk about a free item, the bag is hardly usable as a belt bag since it is so ... baggy.
CONCLUSION
If you ever invest in rechargeable AA/AAA technology, you'll multiply your investment by getting this charger.
UPDATE 7/6/2005:
I've REFRESHed about 8 clunkers so far, 2 NiCads an officemate brought for me to work on (about 2 years old) and 6 Lenmar 2000 batteries.
The results?
NiCad
1 rated at 700, first TESTed at 256, REFRESHed to 677.
2 rated at 700, first TESTed at 344, REFRESHed to 741.
NIMH - done REFRESHing.
1 rated at 2000, first TESTed at 448, REFRESHed to 1507.
2 rated at 2000, first TESTed at 527, REFRESHed to 1820.
3 rated at 2000, first TESTed at 680, REFRESHed to 1488.
NIMH - still REFRESHing.
4 rated at 2000, first TESTed at 435, REFRESHed to 1270+.
5 rated at 2000, first TESTed at 436, REFRESHed to 1713+.
6 rated at 2000, first TESTed at 349, REFRESHed to 1813+.
More Room for Improvement?
Charging Rate Limit (wrt Terminal 1)
The charging rate selected for Terminal 1 (1-4 left to right) is the highest rate you can select for each of the 4 Terminals. I didn't think this would be a big deal, but when you REFRESH batteries at the gentlest rate (200mah charging, 100mah discharging) and the cycle may repeat as many as 20 times ... well, you do the math. I know I didn't have to set it at the gentlest rate, but I figured I shouldn't stress already marginal batteries.
Now, when the battery in Terminal 2 read full (as in Fully Refreshed), I took it out to charge one of the other batteries I had already used up. Enter the Charging Rate Limit. I am limited to 200mah charging (the current setting for the still REFRESHing battery in Terminal 1) and it's driving me nuts! I wish each Terminal had it's full 200-1000mah charging rate available independent of the settings on the other Terminals. La Crosse Technology BC-9009 AlphaPower Battery Charger - Rechargeable Batteries - Charger - Battery Charger Aa Or Aaa - Nimh'
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