How should I charge my eneloop batteries?

Basic charging information and FAQ

Basic info and charging FAQ

 

What does mA and mAh mean ?

mA is the unit (milli Ampere) used for the charging current, which you can compare to "the speed of charging". How higher the mA how faster a battery is charging. mA is also used for the discharging current.

 

mAh stands for milli Ampere hour. This refers to the amount of energy (charge) that a battery contains.  On every eneloop there is a mAh number written. This is the total energy/charge the battery can contain. 

What is the difference between mA and mAh and how do they work?

So how does it (not) work?

Let`s take a standard eneloop with a capacity of 1900mAh.
When you have a charger that uses a charge current of 100mA, the battery will be fully charged in 19 hours.
19 hours of 100mA = 19*100=1900mAh
This is an simple way of explaining, but not really the way mAh actually works. 

 

Why not?

 

It`s the opposite:
To simplify it, you take a battery with 1900mAh and a device (let`s take a flashlight for example) that uses a low current of 100mA. The battery will take 19 hours to discharge the battery from 1900 till empty.
So 19hours discharge at 100mA equals 1900mAh.

 

Isn`t that the same? Why can`t you use that with charging instead of discharging?

Let`s go back to the first example. A batterycharger uses a current of 100mA. When you charge the battery for 19 hours you will have 1900mAh. This is also written on a standard eneloop, so the 1900mAh of energy is now inside the battery.
But

Now you extend the time to charge a battery to 25 hours.
This would imply that you do 25*100mA is 2500mAh. This is the problem! A 1900mAh battery can only hold 1900 mAh even if you put 2500mA into it.

Still not sure?

Try to compare it with a 1-gallon jug. Fill the jug with 1 gallon of water and it will be full. When you continue throwing more water into it, it will still only be 1 gallon inside the jug.

When you empty the jug, only 1 gallon of water would come out.

 

This is a very basic way of looking at it. In real life the mAh depends on a few more things, like the discharge current that is being used and the temperature. More on that in the Advanced charging section.

What is the recommended charge current for eneloops?

The recommended charge rate depends on the model and size. Have a look at all the product sheets on the overview page.  There you will see the fast charge current.

It`s better not to charge at a very low current because it is more difficult for the charger to recognize if a battery is full.

For AA I would recommend anything between 500 and 2000mA, including std, lite and Pro.
For AAA between 300 and 750 mA for std and Pro and 200-500mA for lite.

Are you worried? 
Get a good Panasonic charger.

Panasonic`s smart chargers use normally a charge current of about 500-1000 for AA and 300-500 for AAA.  They are designed for the task, so please sit back and relax!

What chargers should I stay away from?

Eneloop batteries can generally be charged with any kind of NiMH battery charger. But to keep things simple, you better stay away from these 2 kinds of chargers. 

  • Ultra Fast chargers
  • Dumb chargers

Why?

Ultra Fast chargers use a very high current to charge your batteries. This means that the current will exceed the maximum charge current advised by Panasonic by about 2-3 times. Check the PDF product sheets for the recommend charge currents on the Overview page per battery model.

A side effect of charging at a high current is heat. One thing that batteries in general don`t like is heat.

Especially eneloop PRO cells do not like to be charged hot. This will reduce their life cycle!

2 Examples of the 15-minute chargers.

 

Dumb chargers charge batteries for a set amount of hours. Often they will only charge batteries in pairs. This is not recommended.
Eneloop lite AA have a minimum of 950 mAh, and eneloop Pro AA have a minimum of 2550 mAh. Imagine a charger charging at 100mA for 16 hours, this would highly exceed the capacity of the eneloop lite. And not enough for filling up an eneloop Pro.

What charger do I need then?

What you want is a smart charger.

Smart chargers can detect when a battery is fully charged and usually have a back-up cut-off using a timer. (See the Advanced section for detailed information) This will prevent damaging the batteries to a minimum.
They also charge cells individually so you can remove or add another battery during charging. You can also mix AA and AAA batteries in the same charger as it will look at the individual bays.

My recommended simple chargers:

Depending on your specific requirement, as for a simple charger I would currently recommend the Panasonic BQ CC55 for eneloop standard and PRO. It will charge relatively fast and uses colored LED lights to show whether a battery is empty, still charging, fully charged or damaged. This is great for people who don`t want to wait for a long time, and want a clear indicator that batteries are charging, or full. This charger is not recommended to use with Lite models.
There is a video on Youtube in Japanese as well as in English that will demonstrate the ways this charger works.

The Panasonic BQ CC17 is also used a lot, but is quite a bit slower and older. If you don`t care about the charge speed this could be your option. Please look at my eneloop battery charger overview page for more information on all chargers made by Sanyo and Panasonic.

If you are more of a geek take a look at the intelligent analyzer chargers like the Powerex Maha MH C9000, Opus BT-3100/3400, SkyRC MC3000 and the like. These chargers can refresh your batteries, and check the capacity! More about this in the Advanced section.

Oh no! My charger charges till 1.5 V. I thought it should be 1.2V. What is the maximum voltage?

1.2 V is the typical voltage under load. Eneloop AA batteries are mostly charged till about 1.5 or even 1.6V. After the batteries are taken from the charger, the batteries will slowly drop in voltage. So charging till 1.5 V is not bad by itself. See below picture from the Panasonic website . The somewhat horizontal line is under load and about 1.2 Volts.

Why does my charger sometimes stop at 1.6 V and sometimes at 1.45 V?

That is possible. It depends on the battery you charge, how often they it is used. And also the ambient temperature. If you charge them in a very cold room, your Voltage will be a bit higher than in a warm room. Please take a look at this graph below that is taken from a 4th generation eneloop standard, product sheet. You will see quite a difference in Voltage in relation to Ambient temperature.

 

MORE COMING SOON!

If you want me to answer a question, feel free to email me at chibim @  eneloop101.com

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