This is a battery box that allows the use of gum batteries in the WonderSwan, WonderSwan Color, and SwanCrystal. Compared to using dry cell batteries, the main body becomes flatter and easier to hold. This is especially effective when using vertical screen software. Battery life is approximately 3 to 2.5 hours on a WonderSwan Color with an IPS screen installed (depending on the battery condition and other environmental factors). Important Notes: In addition to this product, you will need gum batteries and a charger for gum batteries to use it. Do not use the WonderSwan's dedicated charger. Charging the gum batteries while they are in the battery box may cause the battery box to deform due to heat generated during charging. Since it is manufactured with a 3D printer, there may be slight variations, and it may be difficult to attach to the WonderSwan main body depending on the individual unit. This listing is for the battery box only. Gum batteries and the WonderSwan main body are not included.