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Hi Sandra,
A battery pack will definitely improve your observing time and as Allan pointed out, if you end up getting some dew removal accessories, a portable battery power pack is the way to go.
The three star alignment is not really necessary, the third star is just a confirmation that you have chosen the first and second stars correctly. Once you get to know the sky better you can use the "two star" or "two star auto" alignment procedure.
There are iphone apps and computer programs that help to determine the best stars for alignment but if you follow these couple of rules then you should get very good alignment procedure results.
1) Choose two stars that have a wide angular separation, i.e. are as far apart from each other as possible. You don't, however want ones that are too close to the horizon, anything below 10-15 degrees from the horizon isn't very good.
2) Try and pick the two stars so that a line drawn from one to the other passes as close as possible to the zenith (the point in the sky directly above you).
3) Try not to pick any star that is near the zenith, stars about 10 degrees or less from the zenith can affect the way the software has to calculate position due to how the encoders work.
4) I often find that choosing two stars that cross over the celestial equator can be beneficial to prolonging alignment, though your mileage may vary.
Hope this helps,
Simon
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