ORIGINAL: altavillan

There's a few posts listing lipoly's as needing to be charged outside the plane. I think people are lumping all the batteries in the same bunch. Yes we all agree Li-poly batteries have a higher chance of catching fire if mis handled. Typicaly from over charging or damaged from a crash or droped. Ther is other Li- batteries with near equal power to weight. A few I know are the Li-fe, Li-ion,( Fromco) Li-ion Manganeese.(Duralite) I know I am not giving their entire name but their generic comonly used name. These batteries are advertised as being fire safe or safer than Li-poly and generaly accepted as being as safe as Nicad and safer than NiMH. I've had NiMH swell up and get hot for absolutely no explainable reason.
Choosing a Li- battery other than Li-poly over a123 would be for the weight savings. A123 is a heavy battery. Choosing Li- batteries is for those who want to go to the field and not have to worry about recharging. Since they weigh about half what a a123 weighs you can fly twice as long with them. Draw back to the Li- batteries is their finickyness when charging. Fast recharge dramaticaly reduces their life span. Evan when re-charging them slowly, say .8 amps for a 25c 2500 mah battery, they will typically start to degrade or die completely at around 100 cycles. And expect re-charges to take upwards of 3 hours. Another caution for li- batteries is do not let the voltage get too low. Once they get below a certain voltage they have a tendency to die. Making Li- batteries a potentialy costly learning experience.
The smaller 1100 mah a123 batteries allow the use of a light weight battery in a large plane. Evan though they have a small capacity, they have a tremendous amp output. Plenty powerful for a 30% gasser. Ounce for ounce, greater than all but the most exotic and very high priced Li-poly batteries. The small capacity means frequent re-charging, but thats the beauty in them. No other battery comes close to the a123 batteries ability to re-charge so quickly. They seam to opperate better the harder they are recharged. So plan on throwing at least 4 amps at them.
Most folks claim a 1000 cycle lifespan for the a123 battery. I'm all for that.
Other benefits are numerous, such as, their lower voltage allows their use with just about any servo. No regulators needed. No reports or advertised warning of potential fire hazard. Constant high amp output keeps the chance of a computerised rx from rebooting due to power starvation at a minimum.

Sorry for the long sermon. There are a few threads here on RCU explaining lots more about these batteries. So you don't buy twice or get stuck with a system you don't like read and learn all you can before picking which type of battery you will power your plane with.