These types of rechargeable 'AA' batteries are a replacement for the non-rechargeable batteries, however the batteries they often replace are 1.5 volts 'per battery' and these are 1.2 volts per battery. So if you have a toy that takes, say, 6 of these batteries, it's at 1.5->9 volts. Keep in mind that a 1.2 volt battery is very quickly 7.2 to 6 volts total. So some devices don't like that at all even 'almost full' (like my Korg kids piano with 6xAA). So look carefully at what you use it for or whether this type of battery will work. Sometimes it doesn't work at all, sometimes just fine. Not at all in the case of my Korg children's piano. But maybe other electronics.