In the manual you will find. BN-V416U (2 HR.+) ; BN-V428U ( 4 HR.+) ; BN-V840U (5-6.5 HR.+) ; BN-V856U (7.5-8.5 HR.).
The Last 2 may require a cable & special charger. I have 2 of the BN-V428U these are the largest regular battery. They work exceptionally well. You can be charging your BN-V408U while using the BN-V428U etc. this is great for long shoots. I bought mine at Camera World but also check B&H. Good luck.