As a general rule a 3 cell lipo will weigh about the same as a 7 cell nimh battery but have twice the capacity. For example, a 3 cell 2000ma lipo will weigh about the same as a 7 cell 1000ma Sub A nimh pack. This means about double the flight time. However, the lipo will also have a higher voltage for more power...and hold that voltage more constantly through the flight until just before low voltage cutoff kicks in, where as a nimh will constantly show decreased power as the flight goes on. Both do this but you will notice it more on the nimh.

Many brushless motors require a 3 cell lipo to really shine and show off what they are capable of. While you can power them with nimh packs, you tend to need an 8 or 9 cell nimh pack to get the voltage to where it needs to be, and of course as you add more cells to keep up with the lipo you'll gain more weight.

For the most part, one lipo charger isn't going to give you a better charger over a less expensive lipo charger. Lipo chargers have to follow strict guidelines to safely charge a lipo and as a result there isn't much wiggle room between charging methods. The only exception to this being chargers that balance the cells as they charge. I prefer a balancer that is independent of what lipo charger I'm using. That way if the charger breaks later on I can still you my balancer with another charger. I prefer the Blinky Balancer sold by Astro and promoted by Common Sense to use with their packs (they feature a balancing plug that Blinky plugs into). You can use the balancer before, during, or after a charge. It's about the size of a credit card, requires no power source, and sells for around $25. For a charger I very much like the Celectra 1 to 3 cell charger (They also sell a 1 to 2 cell version).

For lipos I go cheap as possible. Most lipos come from China and are slapped with a "brand name". Much of what you are paying for in the price is name recognition in my opinion. For bottom line prices try Common Sense RC, Dymond Motorsports, or for even cheaper ones try Ebay. Just make sure if you do plan to use a balancer to buy lipo packs with a balancing plug...and one that matches, or buy the proper adaptor to mate them with it.

Yes, lipos can be very dangerous...but so can nimhs and nicads if they are abused as well. Make sure your ESC has the proper cutoff voltage set for a lipo (Lipos don't like being overdrained). Make sure your charger is set to the proper number of cells and never go over 1C (1X2000ma=2 amps on a 2000ma pack). Charge the pack on a cement floor in the open where it can't throw a spark onto something. Don't dent or cut the pack. If the pack shows signs of bloating get rid of it right away. Always remove the lipo from the plane when not in use (the RX/speed control can continue to drain the battery down even if the motor isn't on). If you get your plane stuck in a tree make every effort to retrieve it as soon as possible or the lipo will be drained beyond repair. When not in use store your lipos in a fire box or in an open area on cement. Make every attempt to keep the battery leads from shorting, using heat shrink tubing and electrical tape for insurance.

That all being said, I've seen nimhs catch on fire, overheat, etc....due to overcharging or shorting the pack. Heck, even a D cell battery can cause a fire in your house if it's shorted. I won't be going back to nimhs for most of my planes. The flight times and power a lipo produces will spoil you for life. These batteries, along with brushless motors, are sounding the death bell for gas in my view.

By the way, if you are looking for a cheap brushless motor with great performance check out the BP21 from Balsa Products (Cheaper elsewhere). It's a good replacement for a 400 to 480 sized brushed motor and is going for under $20 now.