Turbo boost is enabled by default. If your BIOS supports disabling it then you can disable/enable all you want by entering BIOS on boot and changing the setting. Maximum Turbo Boost is reserved for a single core only. 2-3 cores can boost to somewhere in between the base clock and the max boost clock. So you won't see the turbo boost speed on all cores at the same time; UNLESS your motherboard (laptop) supports ENHANCED Intel Turbo Boost, which is another setting you can simply enable/disable in BIOS. But the ability to change the setting depends on the manufacturer of the motherboard and if they allow it.
Turbo boost is enabled by default. If your BIOS supports disabling it then you can disable/enable all you want by entering BIOS on boot and changing the setting. Maximum Turbo Boost is reserved for a single core only. 2-3 cores can boost to somewhere in between the base clock and the max boost clock. So you won't see the turbo boost speed on all cores at the same time; UNLESS your motherboard (laptop) supports ENHANCED Intel Turbo Boost, which is another setting you can simply enable/disable in BIOS. But the ability to change the setting depends on the manufacturer of the motherboard and if they allow it.
Yes, turbo boost will have an affect on battery life, but it's pretty hard to say how much (if at all) it'd be noticeable to the user). As said above, it should be on by default, and you may or may not be able to disable/enable it in the BIOS.