From what I recall, the original Game Boy uses a linear regulator so is wasting 20% of its power budget to heat as it converts 6V supplied by 4 AA’s to 5V used

From what I recall, the original Game Boy uses a linear regulator so is wasting 20% of its power budget to heat as it converts 6V supplied by 4 AA’s to 5V used by the electronics. (Hand waiving the numbers here.) Modern power regulators are much better 40 years later. A casual search reveals kits like this one https://handheldlegend.com/products/3-3v-voltage-regulator https://handheldlegend.com/products/3-3v-voltage-regulator which could buck/boost a variety of voltages - even letting you run on 4x 3.6V lithium batteries in AA form factor: https://www.batteryjunction.com/plc-ls14500-ba.html https://www.batteryjunction.com/plc-ls14500-ba.html I’m not sure if the power savings by switching regulators are greater than switching carts but are in the same ballpark and are worth exploring if one is going to these lengths to begin with. Certainly combined with those lithium cells it would make cart selection irrelevant.