Tim Bray is wondering if it would be better to drop the charging circuit from a laptop:

So if this laptop came with two batteries, and an external battery charger that charged faster than the computer ran the batteries down, I could routinely work without having anything plugged in. Also, the laptop wouldn’t have to include the battery-charge circuit, which might allow it to be simpler and lighter.

Anybody who has a small laptop is already carrying around one extra box, namely the power supply adapter, and most of us also carry around an extra battery. Why not make the two of these into a single extra box?

…Are there any Electrical Engineers out there with an educated opinion as to whether losing the charging circuit would make the laptop noticeably smaller and lighter?

In the past, I did some design of battery-charging circuits for portable embedded systems, and in the specific case of laptops I’d say there’d be no savings. My current iBook/600 has a built-in charging circuit but no extra battery to keep things working while swapping batteries. (Previous PowerBooks used to have such a battery.) In my opinion such a battery would be at least as expensive, and use up as much space and weight as the charging circuit. And I find it faster to just plug in a charger whenever my battery goes low, rather than put the laptop to sleep, take a battery out, and plug in a new one…

Other options would be to have the external power supply also have a socket for charging an extra battery (upside: one less box to carry; downside: larger & expensive charger, more connectors, wasted space for people who don’t have an extra battery) or to have parts of the charging circuit built into the battery itself so you can cascade several batteries (upside: more flexibility, simpler charger; downside: more expensive batteries, still need a backup battery inside the laptop).

I think we’ll see some better laptop solutions in a couple of years. Once OLED screens and better polymer batteries come onto the market, we’ll have thinner screens and smaller power requirements. The battery will be a thin slate mounted behind the screen; you’ll get better heat dissipation too and the ability to slap on several batteries if necessary.