i need lithium poly for my GWS IPS_A motor. i use 8.4 volt battery now but i can't find 8.4V li-po.
all they have is 7.4V. why? is 7.4V li-po good for me? what is the differents between lithum poly and lithum ion?? HELP ME!!!!!!!! []

Batteries are made up of one or more individual cells. Each cell has a voltage. NiCd and NiMH cells are rated at 1.2 Volts per cell, so 7 of them connected together in series make 8.4 Volts. Each time you add a cell, the Volts jumps by 1.2.

LiPoly cells are rated at 3.7 Volts per cell. Connect 2 of them together in series and you get 7.4 Volts. Connect 3 cells together in series, and you get 11.1 Volts. Each time you add a cell, the Volts jumps by 3.7.

A 7.4 Volt LiPoly will work fine in place of an 8.4 Volt NiMH or NiCd. It is lighter than the NiCd or NiMH battery, so you don't need as much power. The power difference is very small, anyway.

If you get the new High-output LiPoly cells you will probably find that you get more power out of the 2 cell LiPo than you do from an 8.4v NiMh. I replaced my 8.4v 350Mah NiMh with an 860MahA Thunder Power 2S1P in my Tiger Moth and the difference is incredible. Flys like a whole new plane!

The LI Poly's we use charge up to 8.4 volts for a 2 cell pack. Most fully charged packs will read about 8.5 volts just off the charger.
The 7.4 volt Li Poly is just what you need, will make a big difference. Remember that it needs a different charger, well worth it.

one of my intructors had a 8.4 volt li-po. its good like any other li-po, but i only hd about 15 minutes of flight. i thought li-po can give up to 50 minutes of flight? Is it because i used too much throttle?

Your flight time will depend on capacity of battery, type of motor (size and current draw), weight of plane including wing loading, and flying style.
Take my Mini IFO for instance. I'm flying it with an IPS-A and a 2cell 950mah Li-poly. I get about 15 minutes of aerobatic flight before power really fades. Now if I put on a 2cell 2100mah batt, I could get much more flight time, but the plane wouldn't be near as fun because the 2100's weigh much more than the 950's. The plane would require more throttle to maintain flight, and all manuvers would also require more throttle. It's a balancing act. Generally with an IPS powered plane, I'd stick to a smaller pack to keep it light. Besides, 15 minutes of aerobatics, is about all I can handle.