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Old Nov 16, 2006, 9:44 AM   #11
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I have a Duracell 30 minute charger and it came with 2100mAh batteries. It will charage for 30 minutes before the indicator goes off and safety timer kicks in at 40 minutes.

It does not fully charge 2500 or 2700mAh batteries. I like the performance of this charger in general. Faster than a one hour, but not quite as hard on the batteries as a 15 minute.

Restart, charge twice.
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Old Nov 27, 2006, 3:38 PM   #12
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SilverFoxCPF wrote:
Faster charge rates are more efficient than slower ones, and you are somewhere in the middle with this charger.
In this sentence, what does "efficient" mean? Higher total charge?
With my MH-C401FS, I've been charging on the slow setting, after reading that it would prolong battery life.
Should I?
My Powerex batteries are three years old, and I'm thinking about switching to Eneloops.
TIA, Rick
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Old Nov 28, 2006, 11:43 AM   #13
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Hello Rick,

Let's start with a 2500 mAh cell. When charging at a slow 0.1 C rate of 250 mA, it will take roughly 14 hours to come to a full charge from empty. If things were 100% efficient, it should only take 10 hours, but since they aren't, it takes roughly 40% more charge time.

Now, let's look at a faster charge rate of 1 C or 2500 mA. You now find that it takes around 66 minutes to come to a full charge. At 60 minutes you should be full, but because if inefficiencies, it takes around 10% longer.

As you can see, 10% overcharge for a full charge is more efficient than 40%.

If you go on to a faster rate of 3 C or 7500 mA (this is the charge rate used in the 15 minute chargers), you only need around a 5% overcharge to get a fully charged cell.

Battery life predictions by the battery manufacturers are usually done at the slow 0.1 C charge rate, however some use a 1 C charge rate. When charging at the 0.1 C rate (and discharging at a 0.2 C rate), you can expect to have roughly 80% of your initial capacity after 1000 cycles. When charging at 1 C (and discharging at 1 C), the cycle life drops to around 500 cycles. When charging at 3 C (and discharging at 1 C), the cycle life is dependent on the initial capacity of the cell. 2500 mAh cells are good for about 125 cycles, 2000 mAh cells are good for around 200 cycles.

The battery manufacturers recommend charging in the 0.5 C to 1.0 C range, when using a smart charger that terminates the charge on - delta V (most chargers are using this termination method). This charge rate gives a strong end of charge signal and decent cycle life. You can get improved cycle life by charging at 0.1 C, but you have to terminate the charge with a timer, and this method does not work well if you only partially depleted the cell.

The Eneloop cells can be charged at any of these rates, but you will get better cycle life if you stay within the 0.5 C to 1.0 C charge rate.

The 15 minute chargers offer convenience and many people are willing to sacrifice cycle life for the time savings of rapid charging. If your camera gets 500 shots on a charge, it may not be unreasonable to have to replace your batteries every 50000 to 60000 pictures... After this many shots, you may also have to replace your camera as well.

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Old Nov 28, 2006, 12:32 PM   #14
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If I read the MH-C401FS specs correctly, it looks like the rapid charge falls within the .5 to 1.0 recommendation at 1.0, and the slow charge falls below at .3 (for AA.) I guess this is a reason to use the rapid rate.

Further, if I had read your comments about cycle life three years ago, I would have been using the fast rate all along.

When I was new to the camera and to charging, I purchased about three times the batteries that I needed. Therefore, most of the recgarges that I've done have been because most of the batteries had been sitting on he shelf for a month. That took lots of time at the slow rate.

I guess I'll (1) switch to fast, (2) discard those that seem to be the lesser batteries, and (3) start the switch to Eneloop.

Thanks again, Rick
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