[different rechargeble batteries]

Hi,
i want to know about the mechanism of rechargeble batteries.
why different circuits should be used to charge them?
SO please give me some stuff on it,also some useful links could help me! ???

[using a2 astable multis to build a simple fm comm system]

[glow=red,2,300]hi,[/glow]
I just got an idea to use 2 astable multis to build a simple fm communication system

this uses 1st multi as voltage to freqency converter to convert the input from mic into corresponding frequency of pulses then transmit it.

then at receivers end we use another multi to convert the pulses from antenna to
vo;tages by applying the pulses to the collector of the transistor of 2nd astable multi.(ie., using the bilateral property of the astable multi used as frequency to voltage converter) the feeding this analog voltage to a speaker via amplipfiers.

this makes a simple fm communication set. believe it works .,!!!!
am I right!!!! ;)