(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. Panasonic acquired a majority stake in Sanyo in 2009, and Eneloop batteries were thereafter branded, but not manufactured, by Panasonic. Eneloop cells lose their charge much more slowly than the 0.5–4% per day loss of previously available NiMH batteries, retaining about 85% of their charge for a year after charging; This allows them to be sold precharged. Since then many other makes of NiMH batteries are supplied precharged, with long charge retention. Since Sanyo introduced the Eneloop, many other brands of low-self-discharge batteries became available, described as "low self-discharge","LSD", "pre-charged", or similar. By 2020 most NIMH batteries available were of this type, with varying capacity, self-discharge rate, and lifespan. Those made in Japan are all made in the same factory, but not necessarily to the same specification as the Eneloop brand. There are also counterfeits of Eneloop and other well-regarded brands. Because they can replace a large number of alkaline batteries over their life cycle, Eneloops are marketed as being eco-friendly. History 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. Panasonic retained the "Eneloop" trademark, sourcing the batteries from FDK (formerly Sanyo) factories. Technology After NIMH rechargeable batteries were introduced, they were developed to increase capacity. This was done by using thinner insulators internally, allowing more of the active components to be used and thus increasing capacity. The thin insulators allowed significant leakage, leading to relatively short self-discharge times. Eneloop batteries were designed in a way that traded off somewhat lower capacity for much slower self-discharge. The trade-off was modified for the Eneloop Pro series, providing higher capacity but with more self-discharge and shorter lifespan. The Eneloop Lite series traded significantly lower capacity for longer lifespan, and also faster charging and lower weight. Variant description The Eneloop is the standard general-purpose cell. The cheaper Eneloop Lite has lower capacity and a longer lifespan in charge cycles, but the standard and Lite of about the same time have very similar total lifetime capacity in watt-hours. The more expensive Eneloop Pro has significantly higher capacity and is suitable for higher-current applications, but has poorer charge retention and shorter