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Buying a Nimh battery charger for a walkman. and later on, maybe a camera.

My NiCad batteries were pretty much dead, so I decided I would get modern and buy Nimh batteries. For anybody knowing nothing about batteries, or even electricity, shopping for a charger is really brain numbing. Some chargers come with 2500 mah batteries, some other don't utter the word "mah", some say they protect the batteries with a timer, others have an auto shut-off. Some are big heavy destop models, some are just a little flimsy casing hardly weighing 1/10 the batteries. Etc. And, of course, salesmen know nothing on the matter.

I only intend to charge AA batteries, so I went for an Energizer CHD (chdcwv-4) charger with TA DAM! 2500 mah batteries. Then, I came home to try to find out what I had bought.

First, I learned that, compared to 2000 mah batteries, 2500 mah batteries do last about 25 % longer, but they can only be charged half as many times, 300 to 400 times, Energizer told me on the phone. Then, the silly timer... is just a timer. If the charger is accidentally unplugged, if there's a power failure or the circuit is overcharged and the breakers go off, the silly timer goes on again and the batteries will receive power longer than they should. (Is this why it is recommended not to use the charger with an extension cord?) The same goes I suppose if the batteries are put in the charger without being totally drained: they will be overcharged. Because the charger charges slowly, it shouldn't be dramatic, but it still shortens the life of the batteres, I suppose.

This is not what I wanted. I use batteries mainly for my little Sony walkman radio. (With good headphones, the sound is not bad at all!) It drains very little power, but I often forget to turn it off because when there are ads or silly music, I just drop the headphones down my ears and I sometimes remove them without checking if the radio is on. I also listren to music before I go to sleep. So I wanted batteries that lasted longer than NiCads, but I'm sure 2000 mah batteries would fit the bill.

I also read that low mah batteries were recommended for appliances that require little current, such as my walkman. Is there any chance 2500 mah batteries could damage it?

I don't care about batteries being charged slowly. 12 hours is OK to me. I might some day buy a digital camera but, for now, a desktop charger would be OK. I dont' need to travel with the charger. But, mainly that Nimh batteries have no memory, I'd really like to just drop them in the charger whenever they're not fully charged and just forget about them.

Energizer told me that even the big desktop models work with a timer and that in order to have auto shut-off, I'd have to get the 15 min. $50 dollar model, which makes no sense to me.

So what kind of batteries/charger would you get if you were me? (I can return the unopened package I bought.) I also read that Nimh batteries lose about 4% of their charger per day, True?

Because Energizer, Rayovac and Duracell also sell non-rechargeable batteries, I feel they overcharge :) for the charger and batteries so that it's not so much of an advantage to buy rechargeable batteries. (Yes, I'm sure those little crappy casings called chargers are worth next to nothing. Shit, it seems the MIT will soon provide Third World countries with laptop computers at $100 apiece!) Any other good chargers at a cheaper price from other manufacturers?

Bernard

Reply to
Bernard Sawyer
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Look for a charger by Maha. Their business is rechargeable batteries and their chargers monitor the cell voltage (or rate-of-change, depending on the type of battery) to provide a proper charge. No timer, just smart chips. The latest Maha chargers can handle 1 to 4 AA or AAA cells and have separate detection circuitry for each cell. These chargers aren't cheap, but they won't damage your expensive rechargeable cells.

2000mah NiMH cells charge in a couple of hours with my MH-C204F (several years old). When the cell is fully charged, the charger switches to a maintenance charge level.

John

Reply to
John

Try Sanyo 2100mAH AA cells.

Reply to
CWatters

Fewer cycles from 2500mAh cells are misleading for total usable capacity. Cycle count is based on reaching a percent of usable nominal capacity Although actual capacity depends on the load, and charging etc.., usable total capacity is in favor of the higher capacity cell when today's current loads are considered..

An example using simple linear approximations and a conservative

80% of original nominal capacity as a cycle count limit with each cycle being full a charge-discharge follows with 0.9 being the linear average from 100% to 80% of capacity..:

2500x300x0.9=675KmAh

2100x600x.0.9=1154KmAh

But that's misleading. At 300 cycles the 2500mAh cell has reached a capacity of 2500x0.8=2000mAh and that is essentially the same as the 2100mAh when new so about 600KmAh was free if the cells cost the same originally..

In addition, each cycle is based on discharging at C/10 or C/5 so the 2500mAh cell was providing more power each cycle. And consequently, at 80% of capacity had a lower impedance or open circuit voltage than the new 2100mAh. If the 2500mAh was discharged at the 2100mAh C/10 or C/5 rate, its capacity would increase slightly, perhaps more than the new 2100mAh's..

Net result: higher capacity cells are the better buy if there is no great cost difference ans especially so the the load currents are high..

Reply to
H. Dziardziel

no.

I use a little (pocket sized) Chinese made 12V powered desktop charger, it comes with a cord so it can be used in the car too, (handy if you're out exploiting the cost-per-shot of a digital camera)

this one has some sort of voltage trigger

that sounds excessive

I didn't purchase this one so I can't comment.

--

Bye.
   Jasen
Reply to
Jasen Betts

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