I read that running Ubuntu through a virtual machine such as VMware Player or VirtualBox is actually less costly on a laptop's battery than Wubi because it utilizes Windows' drivers, which are optimized for Windows by the hardware manufacturers, as opposed to the Linux drivers, which are less optimized and thus more costly for your system. Is this true for Wubi? If so, is it also true for a "normal" Live CD/USB installation?
This is not universally true. Some manufacturers/brands of laptops, such as Lenovo Thinkpads, give about equal battery life in Windows or Ubuntu (from personal experience).
- The two big culprits for why Ubuntu/Linux has somewhat poorer battery life than Windows are (a) Nvidia/AMD hybrid/switchable graphics and (b) auxiliary power management (ACPI) such as fans, screen backlight, etc.-
- Most laptop manufacturers will choose to use the cheapest components possible. Since the laptop is bundled with Windows, and the overwhelming majority of its user base will use Windows, the manufacturer often does not bother to check whether these components have adequate Linux support or not. As long as the components come with Windows drivers, that's all that matters.
- For graphics, the Nvidia/AMD refuse to enable the switching capability in their Linux drivers. Consequently, unless you take the extra steps of installing a third-party solution like Bumblebee or vgaswitcheroo -- which may or may not work and aren't automatic -- your discrete graphics are running all the time in Linux/Ubuntu and sucking up power, even if you are doing no "3D gaming" or other heavy stuff.
- Similarly, the stock Linux drivers for things like fan control, screen brightness/dimming, etc. are often inadequately configured and you will have things like the fan running 100% full time, screen not auto-dimming, etc. which also use up power.
Note that everything which applies to a regular/dual-boot install also applies to Wubi. Wubi is only slightly slower/more CPU intensive than a regular install because it stores its filesystem on the Windows partition (NTFS), and therefore I/O has slightly more overhead associated with it.
While a virtual machine may at best be only 90-95% as efficient as a real machine, if your laptop has problems like the above, then yes, virtualization in Windows with the "working" drivers/power management will most probably use less battery than running Wubi/Ubuntu.
Sadly, there's no way to tell how compatible your laptop is until you try it -- spending time tweaking it, use it for a while, ask a few AU questions, etc. to see if you can get great battery life (or not). The laptops that do work well with Linux (Thinkpads, etc.) are usually sold as "business/corporate" machines, and have a price premium associated with them. It's fair though, because I suppose this premium partly enables the use of higher-quality/better-supported internal components.