My device’s battery seems to be wearing down over time. Is this normal, and is the battery replaceable?

Your NIKKI contains a sealed lithium battery that works the same way batteries in modern cell phones work. Over time, all rechargeable batteries slowly wear down and lose some capacity. This is normal for this type of technology. The battery is sealed inside the unit for safety and performance, so it cannot be replaced. The device will continue to function, but the amount of time it stays powered may gradually decrease as the battery ages."