It looks like a good choice. Link to brochure:
http://mediacdn.shopatron.com/media/.../213779785.pdf
If you're able to plug in and let it charge for 24+hrs after deep discharges it should help make it last longer. Try to top it up at least once per month.
Did you find the converter/charger? If not, you might find it by listening for it when plugged in. Mine will make a faint buzzing sound. If the load on the converter is large enough the internal fan will come on to cool the unit and you should be able to hear it.