I have conversion engines but this will be my first engine requiring a ignition battery. I want a battery with atleast a good 2-3 hour flying time on it before it requires a charge. My engine is a SV 26cc Gas Engine CDI 1.75kw
http://www.unitedhobbies.com/UNITEDH...idProduct=5731

You have many possibilities

1. 2300 mah 5 cell Nimh
2. 2300 mah 7.4 volt lipo with regulator
3. Nicad
4. A123

If you have an RC Xcl ignition, an AA cell, 1,100 mAh nicad will give you close to that. About $19.00 at Tower. Definately a low maintenance battery. You can buy something a lot more expensive and a few grams lighter but I don't know why.