In this answer, I've cited the IATA guidelines, which most airlines will likely follow (though deviations are possible).
In summary, you should be fine if your computer's unremovable battery is up to 160 Wh. Current MacBook Pros (as of 2016) should be under 100 Wh.
The Lithium Battery Guidance Document for 2015 states (emphasis added):
Passenger Provisions [p. 12]
220.127.116.11 Lithium Battery-Powered Electronic Devices
Lithium battery-powered electronic devices are permitted in checked and carry-on baggage with the approval of the operator as follows:
(b) portable electronic devices (such as cameras, lap-top computers, camcorders) containing lithium ion batteries as follows:
1. lithium ion batteries with a watt-hour rating exceeding 100 Wh, but not exceeding 160 Wh;
2. batteries must be of a type that meets the requirements of the UN Manual of Tests and Criteria, Part III, subsection 38.3.
18.104.22.168 Portable Electronic Devices (including medical devices) containing Batteries
22.214.171.124.1 Portable electronic devices (including medical devices) (such as watches, calculating machines, cameras, cellular phones, lap-top computers, camcorders, etc.) containing batteries when carried by passengers or crew for personal use, which should be carried in carry-on baggage. Spare batteries must be individually protected to prevent short circuits by placement in the original retail packaging or by otherwise insulating terminals, e.g. by taping over exposed terminals or placing each battery in a separate plastic bag or protective pouch, and carried in carry-on baggage only. In addition, lithium batteries are subject to the following conditions:
(a) each installed or spare battery must not exceed:
1. for lithium metal or lithium alloy batteries, a lithium content of not more than 2 g; or
2. for lithium ion batteries, a watt-hour rating of not more than 100 Wh.
There is also provision, with the approval of the airline, for larger lithium ion batteries with a watt-hour rating in excess of 100 Wh, but not more than 160 Wh in equipment and no more than two spare lithium ion batteries as set out in subparagraph 126.96.36.199 as follows:
188.8.131.52 Lithium ion batteries exceeding a watt-hour rating of 100 Wh but not exceeding 160 Wh may be carried as spare batteries in carry-on baggage, or in equipment in either checked or carry-on baggage. Batteries must be of a type that meets the requirements of the UN Manual of Tests and Criteria, Part III, subsection 38.3. No more than two individually protected spare batteries per person may be carried.