I would get:

*Up to two additional lipo batteries (20 to 30C rating and up to 2200 mAh)
*A lipo charger system
*Lipo balancer (this could be integrated with the charger or a separate piece of equipment....doesn't matter so long as it's used)

The stock charger supplied is of low quality so it is worth it to upgrade for this heli and for any other RC units you'll get down the road using lipo batteries.

The C rating explains how many amps the battery can discharge/charge at.....the higher the better, but a thorough knowledge of battery size and C rating/motor/ESC combinations are a must at some point. These systems are electrical and you need to figure out how it all works in unison sooner rather than later.

The mAh (milliamps/hour) is a reference to battery capacity. The higher the mAh the more "juice" it can store giving you longer flight times between charges.

There are a few more things that this heli could stand to have upgraded such as the speed controller, the servos & gyro.....but for now, being new to this hobby and all, it is OK to use middle of the road gear on this heli and once you become a better pilot it would support spending more $$ on the electronics.