Charging at a slow current can actually be more problematic when the charger can not detect whether a battery is full. At a higher charge rate it is easier for the charger to detect a Voltage drop and Temperature increase and therefore know when to stop charging.
These 2 checks can be missed when the batteries are charged at low current! MA is the unit (mill Ampere) used for the charging current, which toucan compare to “the speed of charging”.
This refers to the amount of energy (capacity/ charge) that a battery contains. A regular white Envelop AA has a capacity of 1900mAh.
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. So 19 h ours discharge at 100 MA equals 1900 mAh.
This is also written on a standard Envelop, so the 1900mAh of capacity is now inside the battery. Now you extend the charge time to a total of 25 hours.
Fill the jug with 1 gallon of water, and it's full. In real life the mAh depends on a few more factors, like the discharge current that is being used, the age of the battery (how much used) and the (ambient) temperature.
This includes a predefined amount of current for charging and discharging, an ambient temperature of X degrees, and a certain amount of rest within their amount of charge and discharge cycles. Imagine how much environmental damage you would have saved by not using Alkaline batteries.
A friend of mine, Viking (a member of the CPF forum) has helped me to understand these testings. There is a test on this website that shows a 10-year-old San yo Envelop still having charge left after 10 years.
Another discharge test can be found here: http://budgetlightforum.com/comment/1477075#comment-1477075 where the batteries in question were 12 years and 9 months old. Envelop PRO will lose a charge quicker, but still only 15% within 1 year.
The recommended charge rate depends on the model and size. 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.
My recommendations for manual chargers; (charge rate: 0.3C-1C). This is also the recommended charge rate by Maya / Powered.
Check the PDF product sheets for the fast charge currents on the envelop lineup page per battery model. A side effect of charging at a high current is heat.
One thing that Nigh LSD batteries in general don't like is, heat. Especially Envelop PRO cells do not like to be charged hot.
Dumb chargers charge batteries for a set amount of hours. Envelop lite AA has a minimum of 950 mAh, and Envelop Pro AA has a minimum of 2500 mAh.
Imagine a charger charging at 100mA for 16 hours, this would exceed the capacity of the Envelop lite. Fortunately they use a rather low charge current and therefore won't damage the batteries as much.
Please take a look at this graph below that is taken from a 4th generation Envelop standard product sheet. You will see quite a difference in Voltage in relation to Ambient temperature.
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 limit charging related damage to a minimum. They also charge cells individually so toucan remove or add another battery during charging.
Toucan also mix AA and AAA batteries in the same charger as it will look at the individual bays. For a simple charger, I would currently recommend the Panasonic BY CC55 for Envelop standard and PRO.
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 using with the Lite model or older batteries. There is a video on YouTube in Japanese as well as in English that will demonstrate the ways this charger works.
The Panasonic BY CC17 is also used by many 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 the Envelop battery charger overview page for more information on all chargers made by San yo and Panasonic. If you are more of a geek take a look at the intelligent analyzer chargers like the Powered Maya MH C9000, Opus BT-3100/3400, Sky RC MC3000, and the like.
Envelop AA batteries are mostly charged till about 1.5 or even 1.6V. Just keep in mind that Envelops do not come from the factory fully charged.
While the Panasonic BQ-CC55 charges 4 AA batteries in about 3 hours. And you could do a refresh on a more advanced charger by setting the MA.
Check out the explanation in the advanced section. It is recommended to set a refresh at between 1000-2000mA for charging and 500-1000 discharge rate for regular (white) AA Eneloops. Some chargers like the Lacrosse BT C700 and Volt craft IPC 1L have problems with refreshing Envelop PRO batteries when set at 200 MA charge.
So better set the charge rate at max, in this case, 700mA. Just charge them up with the charger you have, and put them in an old-fashioned flashlight with an incandescent bulb, run it until they're completely dead, then charge them up again.
You better use a flashlight with incandescent bulb because most modern LED flashlights have different built-in digital power circuitry which will all work differently and probably quit working before the batteries are completely discharged. So at half the charge rate, it's taking 2 hours to fill.
So if the charger senses a change in voltage so that the Voltage drops (which means negative) within X amount of time it will notice the battery is fully charged. See this graph that HK made and look at the Red line.
The problem with low C charge rates is that the Voltage drop is difficult to measure. Instead of measuring whether a Voltage drops, like the aforementioned HDV/DT termination, this one does it differently. When a battery is depleted the Voltage is lower than when fully charged.
When you charge a battery, the Voltage will rise over time. The 0 DV refers to 0 Voltage difference at x amount of time.
As the battery tester HK has pointed out, this type of termination is sometimes difficult to distinguish from a HDV/DT termination. A charger like the Lacrosse BC700 probably uses this termination, especially at a lower current. Although constant current is used often for a longer period, they usually slow down when the battery is almost full.
Some chargers like the Panasonic BQ-CC16 and BQ-CC55 use a 1-hour trickle charge to top off the battery. (However, this is different from a Refresh or Analyze mode)The Maya Powered MH -C9000 for example has a Break-In option.
When using rechargeable Nigh batteries people advise doing a Break-In right out of the package. It's a great feature for old rechargeable AA or AAA batteries that are almost useless or completely dead.
New Eneloopbatteries need a few cycles to get to max capacity... (This is also written in each battery product specifications. Some San yo and Panasonic chargers in Japan (used to) have a Battery Refresh mode.
Some advanced chargers will continue this cycle until the max capacity is reached. An Analysis mode does basically the same thing as it will Analyze the capacity of a battery by charging, discharging, and charging it up again.
At the end of this process, it will show the discharge capacity. Being almost identical to the Refresh mode, it's only called an Analysis mode when the charger has an LCD screen in order to read the capacity and Analyze the results...
You check which Envelops have the closest capacity and use those in an application to protect the batteries from an over-discharge / deep discharge. Say for example a flashlight that uses 4 AA batteries in series.
Start discharge directly after the charge has finished, without a break at 0.25C for 2 hours and 20 minutes Start discharge directly after the charge has finished, without a break at 0.25C for 2 hours and 20 minutes.
Start discharge directly after the charge has finished, without a break to 1.0V When both of these cycles have a smaller discharge duration of 3 hours the test is considered complete.
In the Advanced section at the bottom of this page, I explain what the C-rate means. Imagine a full battery to be 100%. If we discharge a battery at 20% speed of the full capacity it should take 5 hours to empty.
The life cycle test will stop when the battery can't reach 60% of its original capacity during a 50th cycle-set. (the cycle tests are done in sets of 50 charges and discharges as can be read here above).