SearchBatteries

There are lots of types of batteries available for R/C cars. Disposable are usually a really bad idea.

One thing to know about batteries is that they store energy so that it can be released. Typically we want to store lots of energy so that our droids can run longer, go faster, play music longer, flash more lights, etc. But energy is still energy, and if it gets released too quickly, well, that's not good. Any battery can be shorted or whatnot, and the more energy stored, the worse the scenario. However the higher capacity batteries tend to also be more fragile and pickier about charging, etc.

Lead Acid

Lead Acid batteries are what you have in your car. Pretty basic and reliable, but a key part for droid builders is right there in the name "Lead." Lead is heavy, and so are lead acid batteries. They're also bulky. They also don't cycle as well as other technologies, and have a lower energy density. But they can be OK for some purposes.

Besides the obvious problem of carrying the droid around, "heavy" means that your motors will have to move the heavier battery, which means that they draw more power. Which means more batteries. Which means heavier...

Another problem is that the "acid" bit can get outside of the battery, especially if they're overcharged. That can be annoying.

Sealed Lead Acid Batteries

SLA (Sealed Lead Acid) batteries are basically the same idea, but sealed so that the water can't go out and they can't leak. Of course, then you have problems if they get overcharged because they basically have to break and can't be fixed. Alarm systems typically use sealed SLA batteries. They can be a decent choice for a droid, but still are pretty heavy.

Often SLA batteries are chosen for larger droids where more energy is required and the droid is heavy for other reasons.

Nicad Batteries

Nicad (NiCd) are kind of the most basic and a decent choice for lots of R/C vehicles. Most entry level or kid's R/C type cars will have Nicad batteries. They're a good choice and readily available.

LIPO Batteries

Lithium-ion and Lithium Polymer tend to get lumped together, but these are higher energy batteries. They can provide longer lasting droids with higher energy loads, but they tend to be very fragile. Particular care is needed when charging them, and electrical problems can lead to fires or even explosions. LIPO should probably be avoided by most builders.

LiFePO4

Lithium Iron Phosphate batteries are a newer technology. They often require special charging systems, requiring the cells to be equally charged, but tend to be safer than LIPO batteries, though they still store a lot of energy and can therefore become dangerous if mishandled. Good LiFePO4 batteries will have protection circuits built in to help protect against the most serious problems.