Upvote:2
Laptop batteries are usually Lithium ion batteries. FAA regulations state that you may bring up to two such batteries with a maximum of 160 Wh in your carry-on (should be similar in other regions). Your laptop batteries are very likely below that limit. Please note the carry-on part; large Lithium batteries are prohibited in checked-in baggage due to fire hazards.
Addendum: As you're actually forced to take them in carry-on, I wouldn't expect difficulties. Still, if they're not too difficult to remove from the Laptop: in case you get into troubles, you could simply remove one battery, show that the laptop works, insert the second and remove the first and demonstrate a working device again.
Upvote:2
I've taken a laptop with 'normal' battery and external battery slice through airport security multiple times and never had any problems. Although I've also never been asked to turn it on to prove it's not a bomb.