You want the En-el4a and it is worth every penny. It can be used in the MB-D10 on the D300 and D700 if that was your question. I use the 4a in my D2Xs and D300. You will never have to worry about running out of battery with the EN-el4a it is that good. For your light weight travel kit take the grip off and use the EN-el3e. Many people have complained about the cost of the larger battery and its charger. When you spend $10,000 or more on camera gear $500.00 for the battery system is a small price to pay.