The Petzl Nao Plus Rechargeable Battery is for those that will be out for long periods of time and may not have the option of being able to recharge their battery. Having a second recharged battery in reserve is more than a good idea it could be essential for your survival.
This is the battery which comes with the Nao Plus which replaced the Nao in Winter2016/2017. This new battery is also compatible with the older versions of the Nao.
To the Nao software the batteries are individual so not only can you tell them apart you can also set them to discharge in different ways so you could have a running battery and a climbing battery.