Hodgkinson wrote:
A better and more energy efficient solution would be to use some kind of buck/boost converter system (Which I presume is used in laptops) to maintain the rails from a wide range of battery voltages; however that can be complicated and ready-built units of the sorts of current ratings you would require are expensive.
Most indeed are, but check out the offerings of this eBay shop:
http://stores.ebay.com/Sure-Electronics_Prototype-PCBsSpecifically you would need their MC34063 Based Switching Regulator Adapter, Step-Down item.
It's not the first time I bought stuff from this shop, and would recommend them, though I haven't tried this particular power supply.
Granted, it's only step-down and you'd have to use batteries with a high enough voltage to ensure that even when discharging, they keep a stable voltage as long as possible (you need at least 2V more than your required output). On the web there is info about a white LED hack for the PSOne screen to reduce power consumption.
Cheers!
Edwin
