Whatever battery pack you use, it needs to be the same voltage.
If it has more amp hours or watt hours, it should last longer before the batteries go flat.
Having batteries in series, results in a higher voltage.
Having batteries in parallel, results in more amp hours or watt hours.
People often get this confused so I thought I'd add some clarification; Example.... If you have two single cell batteries with the same Ah rating in parallel you will get a set watt hour rating and double the Ah rating. Now if you take the same two single cell batteries in series with the same Ah rating, the total Ah rating remains the same ( does not double ) but the voltage will be doubled. This fact in turn gives you the same watt hour rating as the two like cells in parallel. This is why calculating watt hours is the more accurate way to judge how much run time a battery or battery pack can provide, especially if you happen to know the possible power usage of the lamp you are using. This being said, the more cells you provide either in series or in parallel is going to raise the total watt hours of the battery pack you are using.