can some one please help me with RC cars?

i would suggest you nitro cars..but if your mind is on battery then you chuz! Nitro and battery are both good, now on depends on the type you buying, power, speed, etcccc
References :

Nitro cars will run longer between fillings, you can run them at full throttle longer, they are cheaper to buy, have more power, and they sound really cool. Downside, Nitro fuel is expensive to buy, but a jug lasts a long time. It also can be kind of messy. Have plenty of paper towels handy. The engines can be hard to start, and tune. There also is more maintenance. At the end of a racing day you still have a half hour of work cleaning and oiling to do. And depending where you run, noise can be an issue. Electrics are cleaner, easier to start, run, and maintain. No messin' around, just plug-in and go! Run-time between charges is lower, so you will need extra batteries. And they are expensive. I guess it is a trade-off between labor and expense.
References :

To contradict the two other answers, stock electrics are probably the cheapest RC cars to buy. (Hsp XSTR, Thunder tiger ZT2, Traxxas slash etc etc.) The question is compounded by their really being two classes of electric RC car nowadays.
There is; Stock. Usually cheap to own and maintain, they use between a 13 turn and a 27 turn brushed motor, depending on the chassis. These are the beginner rigs. Usually get them to about 20 mph, set up properly. You can usually find one for under $150. Most will run on nikel metal batteries, which depending on the milliamp rating, will provide between 5 and 15 minutes of play time. There are chargers that 'quick charge' these batteries, so having 3 packs means you can keep yourself amused all day, so long as your near a socket. The batteries are cheap to, being about $10 for the lower milliamp ones.
Brushless; Brushless is a new electric tech that is entirely different to stock. Brushless motors are (around) 98% efficient, compared to brushed motors (found in stock) which are about 48%. This gives greater power for size and much better battery times. Brushless motors require a brushless electronic speed control. Most brushless rigs use 'lipo' batteries. These give a much better discharge rate and run time than nickel metals (a good lipo, well charged can get upto 45 minutes in a tenth), whilst also being lighter. The downside being that they are much more expensive, require specialist balanced chargers, and have been known to explode if you get them wrong. Brushless as a rule is very expensive. However, it is also very swift. The current RC speed record is held by a brushless rig, (google it) and brushless, driven well, can happily hold its own against nitro.

There is also nitro, and petrol.
Nitro; Nitro is an investment in time as well as money. They take a whole lot more looking after than electric. They need to be tuned, oiled, cleaned, serviced. However, i like them. There is nothing more satisfying than tinkering with a nitro, then seeing it absolutely fly round a track. However, be aware that these models will cost you money over time, as bits wear out.

Petrol. Big 1/5th cars. Run on glorified lawn mower engines. Epic expensive to buy, but cheap enough to run. People say they have the best durability, but the 1/5ths down my track seem to have more problems than my nitros.

Final point, the more you spend on a rig in the first place, the better it will be, and the less it will cost in the long run. Buy fron a reputable brand. (HPI, Traxxas, jammin/hong nor, losi, Team associated, Thunder tiger)
References :
Hpi bullet. Hong nor CRT1 buggy. Traxxas Jato. Traxxas nitro sport. Thunder tiger MTA4. Thunder tiger SSB. Brushless HSP XSTR. Brushless acme pioneer. Brushless/stock strada short course truck.