Ack! DSi guts!! Here's a look at the DSi's innards, which might very well explain the portable's lacking battery life. When the specs of the DSi and the DS Lite were first compared, there was a noticeable drop off in juice power: between 1 and six hours.
From the teardown, it seems that the DSi's torqued up processor and speakers get the finger pointing and not the new, larger screens. Bunnie's blog, which did the DSi dissection, writes: "The markings on the CPU package yield no clues about its performance, but my guess is that any ARM9 or ARM11 CPU manufactured in 2007 would have a performance around the 266-533 MHz range." More nitty-gritty and gruesomely fascinating pictures in the link below.