High capacity AA battery pack
Rechargeable AA come in either Nickel-Metal Hydride or Nickel-cadmium

If the battery pack is 4.8 volts the capacity will not increase from a single 1.2 v battery.

If you connect four 1.2v 2000 mAh in series you will have 4.8 volts @ 2000mAh. 

You CANNOT use a NiCd charger to charge NiMH.  NiCd can be charged in 1-2 hours where NiMH require 3-4 hours. NiMH have a low tolerance for over charge.




You can use a NiMH  charger to charge a NiCd.  NiCd are very forgiving and safe.  

If the voltage matches the original batteries, they will very likely work in your car.  A drone or a precision racing model may have some problem due to weight differences. 





Nickel-cadmium (NiCd)

Capacity: 600 - 1000 mAh  1.2v

Pros


Rugged, high cycle count with proper maintenance
Only battery that can be ultra-fast charged with little stress
Good load performance; forgiving if abused
Long shelf life; can be stored in a discharged state, needs priming before use
Simple storage and transportation; not subject to regulatory control
Good low-temperature performance
Economically priced; NiCd is the lowest in terms of cost per cycle
Available in a wide range of sizes and performance options


Cons 


Relatively low specific energy compared with newer systems
Memory effect; needs periodic full discharges and can be rejuvenated
Cadmium is a toxic metal. Cannot be disposed of in landfills
High self-discharge; needs recharging after storage
Low cell voltage of 1.20V requires many cells to achieve high voltage






Nickel-metal-hydride (NiMH)

Capacity: 800 - 2300 mAh 1.2v

Pros


30–40 percent higher capacity than a standard NiCd
Less prone to memory than NiCd, can be rejuvenated
Simple storage and transportation; not subject to regulatory control
Environmentally friendly; contains only mild toxins
Nickel content makes recycling profitable
Wide temperature range


Cons


Limited service life; deep discharge reduces service life
Requires complex charge algorithm. Sensitive to overcharge
Does not absorb overcharge well; trickle charge must be kept low
Generates heat during fast charge and high-load discharge
Hig self-discharge
Coulombic efficiency only about 65% (99% with Li-ion)