Add li-poly battery to projects
Lipoly batteries are good because of their high energy density. There are some alternate chemistries that are worth considering as well, but the idea will be the same.


Battery maintenance:
Maintenance is relatively simple. Do not let the battery die all the way and make sure to buy a balancer/charger. Most lipoly batteries have an extra header used for balancing. Yiu can buy a battery monitor to connect to this. It will beep and flash red when the battery is low.
Battery charging
Lipo batteries will have a "c" rating for charging and discharging. Be mindful of this number because exceeding this number will increase the likelihood of a "thermal event." How do you use the c rating? If a battery is rated at 1Amp-hour and 1C (charging), then the max charge current should be 1amp-hour*1C =1A. Do not overcharge. Typically a battery is 4.2V is per cell, but there are higher voltage batteries. LiFePO4 is 3.3/cell nominal. I think 3.6 charged. For your needs a 2S (2-series) would work well. 
Brands?
There are many, but I really like Turnigy from hobbyking.com. I've had good like with Zippy as well. 
Safety
Lipoly batteries CAN overheat and result in FIRE. There are some countermeasures to this:  


Use fireproof/fire resistant containers when charging and storing batteries  
take swollen batteries to your nearest battery store for safe disposal.  
Add fuses to all devices (uncommon). This is done in cars for the same reason.  
Check LiFePo4 batteries. Slightly lower energy density, but they are less likely to catch on fire.  
Keep a class D fire extinguisher around. This is both a chemical and electrical fire.
There are "hard case" batteries that reduce the likelihood of a puncture. I've only ever owned one, but I did really like it.  
Always monitor your charging batteries. If there's a fire, you want to be there.



I would provide links for you, but my computer died and I'm on my phone. 

Edit: I have this charger and like it a lot