Having a scanner for NASCAR racing allows you to better understand what is going on with individual teams and gives you a better sense of what issues are affecting the race. Buying a scanner can be a daunting task, though. The feature lists runs on and on and if you have never owned a scanner before it can be difficult to tell what is important and what isn't.
Number Of Channels
How many do you need? Models with less than 100 channels are only recommended for occasional race fans as you can't have the whole field programmed in at the same time. 100 channels is really the minimum for the average fan. 200 channels (or more) are best for race fans who attend the entire race weekend. You can put the Cup cars in channels 1-100 and Nationwide cars in 101-200 by car number, and then you won't have to reprogram.
Another factor to be aware of is which frequency bands the scanner can reach. Many scanners can't pick up the 800Mhz channels. While the majority of race frequencies fall in the 450-470 Mhz range there are some drivers up in the 855Mhz band. If your scanner doesn't support the 800Mhz band then you simply won't be able to listen to those drivers.
Some scanners will specifically state that they are "audio modified." This means that they have been altered to boost the volume. My personal scanner is not audio modified, and I don't believe that this is an important feature. If you are having a hard time hearing you should consider buying a higher-quality headset to better block the outside noise.
Some scanners require their own custom rechargeable battery pack while some scanners will take regular off-the-shelf alkaline AA batteries. Rechargeable battery packs require a little pre-planning to ensure that your scanner is charged up before you go to the race but AA battery powered scanners are going to cost you more money over time as you will need to replace them regularly.