There are many reasons why people might choose to have dual batteries in their 4WD. One reason is that it can provide a backup power source in case the primary battery fails. Another reason is that it can help to keep the engine running if one battery dies while the other is still operational. Dual batteries can also be used to power accessories such as lights and winches, which can be helpful when off-roading. Finally, having two batteries can simply give peace of mind knowing that there is a backup should something go wrong.