Eneloop batteries have been around since 2005, although they were originally made by Sanyo and later acquired by Panasonic in 2009. They were somewhat revolutionary at the time, solving a number of perennial problems suffered by rechargeable batteries. Older NiCad (Nickel Cadmium) rechargeable batteries suffered from a ‘memory effect’, so you’d have to discharge them completely before recharging them to retain their full capacity. Specialist battery chargers could do this, but you’d be in for a long wait.
Newer NiMH batteries had virtually no memory effect but tended to self-discharge over a few weeks, even when sitting in a drawer doing nothing. By the time you came to use them, they’d often have very little charge remaining or even be completely flat.
