Eneloop

 (stylized as eneloop) is a brand of 1.2-volt low self-discharge nickel–metal hydride (NiMH) rechargeable batteries and accessories developed by Sanyo and introduced in 2005. The brand is presently owned by Panasonic after their takeover of Sanyo.
Eneloop cells lose their charge much more slowly than the 0.5–4% per day loss of standard NiMH batteries, retaining about 85% of their charge for a year after charging. This allows them to be sold precharged and ready for use, unlike older types.
Because they can replace a large number of alkaline batteries over their life cycle, they are marketed as being eco-friendly.
Sanyo was acquired by Panasonic in 2009. In exchange for US FTC approval of the takeover, Panasonic agreed to sell Sanyo's portable NiMH battery business to Fujitsu subsidiary FDK in order to preserve competition, and later did so.
Following this, Panasonic retained the "Eneloop" trademark, but continued to source the batteries themselves from the same factories (formely Sanyo's, later FDK).
Variant description.
Eneloop.
1st generation.
The original Eneloop batteries were introduced in AA and AAA size, with capacities of 2,000 mAh and 800 mAh. They could be recharged 1,000 times and held up to 75% of their charge after one year. The part numbers for first generation cells are HR-3UTG (AA) and HR-4UTG (AAA).
2nd generation.
The second generation of Eneloop AA and AAA batteries was introduced in 2010. It endured 1,500 recharge cycles and held 85% of the charge after one year and 75% after three years. The part numbers for second generation cells are HR-3UTGA (AA) and HR-4UTGA (AAA).
Sanyo introduced C- and D-sized Eneloop batteries with a minimum capacity of 2,700 mAh and 3,000 mAh respectively in 2009, along with a new universal charger. As these sizes were only available in Japan and Singapore, Sanyo offered adapter sleeves to fit AA batteries in devices that take C or D batteries.
3rd generation.
In October 2011 the batteries were again improved to retain up to 90% of their capacity after one year, 80% after three years and 70% after five years. The batteries can be recharged up to 1,800 times, rather than the 1,500 times of the previous revision. The part numbers for third generation cells are HR-3UTGB (AA) and HR-4UTGB (AAA). At the same time, the C- and D-sized Eneloop batteries' stated minimum capacities were increased to 3,000 mAh and 5,700 mAh respectively. They were available in Japan from November 2011.
European models went on sale from the beginning of October 2012.
4th generation.
Following the acquisition of Sanyo by Panasonic, a fourth generation was introduced in April 2013. The number of charges per cell was increased from 1800 to 2100 cycles for both AA (BK-3MCC) and AAA (BK-4MCC) models. In some countries the batteries are branded as Panasonic.
Eneloop Lite.
1st generation.
The Eneloop Lite line was released in Japan in June 2010. They addressed two disadvantages of alkaline and other NiMH batteries: the initial cost and the long charging time—both achieved by reducing the capacity of the battery. The batteries find suitable applications in low-drain devices such as remote control devices and alarms, where low capacity is not an issue. The AAs have 1,000 mAh of capacity, while the AAAs have 600 mAh. Due to reduction of the capacity compared to the regular Eneloop cells, the charging time is halved for the AA and reduced by 25% for the AAA. On the other hand, they can be recharged 3,000 times. The reduction in capacity also reduced the production cost, which decreased the initial investment for rechargeable batteries. They also weigh 30% less. The product numbers are HR-3UQ (AA) and HR-4UQ (AAA).
2nd generation.
Along with the upgrade of the regular Eneloop cells in April 2013, the Lite version was also upgraded. According to Panasonic, it can now be recharged up to 3,000 times (life cycles) (model numbers BK-3LCC for the AA and BK-4LCC for the AAA battery). The upgraded batteries also retain 90% of the charge after one year like the regular Eneloop cells.
(Eneloop XX).
1st generation.
The Eneloop Pro (or XX powered by Eneloop Technology in the US, Canada, and Europe) series was introduced in 2011. At that time, no AAA version was produced. They have a higher capacity than regular Eneloop cells, 2,500 mAh (min. 2,400 mAh) for AA. However, they retain only 75% of their initial charge after one year, and can only be recharged 500 times. The product numbers are HR-3UWX (AA) and HR-3UWXA (AA).
2nd generation.
In January 2013, Sanyo announced the second generation of Eneloop XX (model HR-3UWXB, or Panasonic BK-3HCC), branded Eneloop Pro. The new generation has a 50 mAh higher capacity (2,550 mAh nominal, 2,450 mAh minimum capacity), and the self-discharge rate was improved, retaining 85% up to one year. They also introduced an AAA version of the Eneloop XX (model HR-4UWXB) with a nominal capacity of 950 mAh (900 mAh minimum). After the acquisition by Panasonic, they were renamed Eneloop Pro (model BK-4HCC) in Europe (BK-4HCCE) and the Americas (BK-4HCCA).
3rd generation.
In October 2015, Panasonic remodeled Eneloop Pro (BK-3HCD/BK-4HCD). The minimum capacity of the battery increased, by 50 mAh to 2500 mAh for AA and by 30 mAh to 930 mAh for AAA.
Eneloop Plus.
Eneloop Plus cells have a PTC thermistor built-in that cuts the power in case of overheating. This makes them especially suitable for toys and devices that generate significant heat. Other specifications are identical to the second-generation Eneloop batteries. The product number is HR-3UPT (AA), and the battery was released in Japan in December 2011.