Yes it is fine for car use. just as stated above make sure it is secured inside the car's battery tray tightly. Soft packs are more prone to puncturing and punctures make LiPo batteries catch fire.
The Zippy flightmax 5000mah 45C 14.8v 4S lipo is one of thee best batteries I have bought from hobbyking! I own 8 of these and not one problem yet,with over 13 months of use on 4 of them. of course every now and then you might get a bad battery, out of all the brands I have bought since the introduction of lithium polymer batteries, these have had the least problems collectively out of any brand! 5 stars and 2 thumbs up!
over 30 years RC racing, building, fixing/diagnosing, and bashing.