How is the cycle life tested for Eneloops? (IEC 61951)
This is rather technical. But every trustworthy battery manufacturer that uses these IEC or JIS standards has to follow these rules:
- Before the battery cycle test is done the battery has to be discharged at a Constant Current of 0.2C which is 380mA for a standard model Eneloop battery.
- The battery cycle test has to be carried out at a room temperature of 20 degrees Celsius +-5 degrees
- The battery should not rise above 35 degrees during the test. If so the battery should be cooled down by forced air draught.
Battery cycle testing is done in sets of 50 cycles, with the following requirements:
Cycle 1: charge at 0.1C for 16 hours. Start discharge directly after the charge has finished, without a break at 0.25C for 2 hours and 20 minutes
Cycle 2-48: charge at 0.25C for 3 hours and 10 minutes. Start discharge directly after the charge has finished, without a break at 0.25C for 2 hours and 20 minutes.
Cycle 49: charge at 0.25C for 3 hours and 10 minutes. Start discharge directly after the charge has finished, without a break to 1.0V
Cycle 50: charge at 0.1C for 16 hours. Rest for 1-4 hours. And discharge at 0.2C to 1V.
- If cell drops below 1.0V during the 1-48th, the discharge may be terminated.
- After the Discharge of every 50th cycle, it is allowed to stop the cycle test until a later time before continuing with the 51st cycle. This is also allowed at the 100th, 150th, 200th, 250th, etc. cycle.
When does the test stop?
When the duration of the 50th discharge cycle becomes less than 3 hours, the discharge test has to be redone according to the specification of the 50th cycle. When both of these cycles have a smaller discharge duration of 3 hours the test is considered complete.
At this stage, the battery can only provide 60% of its capacity. So the cycle test stops at the 60% mark.
See the picture above.
Where do you get the 60% from?
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. Because 5 times 20% equals 100%.
Please understand this before you proceed with reading.
Well, you can compare 0.2C discharge rate with 20%. (see the Discharge Rate during the 50th cycle).
If the 50th discharge cycle ends within 3 hours instead of 5 hours you can calculate the %.
If 100% discharge takes 5 hours, then how much percent will 3 hours be?
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).
More questions about charging (Eneloop) batteries
+ Is slow charging better than fast charging for Eneloops?
+ What do mA and mAh stand for? And what’s the difference?
+ How many times can Eneloop rechargeable batteries be recharged?
+ Do Eneloop batteries need a special charger?
+ How long do Eneloop batteries hold a charge?
+ What is the recommended charge current for Eneloops?
+ What’s the best Eneloop charger?
+ Eneloop Voltage – what’s the deal
+ Can you overcharge Eneloop batteries?
+ What is the maximum charge voltage for Eneloops?
+ Do I need to charge my new Eneloop batteries before I start using them?
+ Should I discharge my Eneloops completely before charging them?
+ How long does it take for Eneloop to charge?
+ How do I need to Refresh my Eneloops?
+ Can I refresh Eneloops if I don’t have a charger with a refresh option?
+ How many years do Eneloops last?
Advanced Eneloop charging info
+ What is -dV/dt charging? (termination)
+ What is 0 dV/dt termination?
+ How are Eneloops tested to claim a 2100 cycle life? (IEC 61951/ JIS 8708)
+ Non-charge related questions can be found in the Eneloop FAQ