There are 6 battery chemistries are in practical use today: 

 Nickel Cadmium (NiCd)

 Nickel Metal Hydride (NiMH)

 Lead-Acid (VRLA, AGM GEL)

 Lithium-Ion (include Lipolymer) 

 LiFePo4 battery types.

Generally, smart chargers have 4 basic charging stages: pre-charging stage, bulk charging stage, trickle charging stage and maintaining stage.

Pre-charging Stage:
   

 When a battery is full discharged and almost empty, a small charging current pre-charging stage will be necessary. The pre-charge current generally is set as 0.05C about.

For example, if you have a 14.8V 2000mAh Li-ion battery-pack, when this battery is full discharged, it is better to select 0.05x2000=100mA as the pre-charge current. After apply 100mA to this empty batter-pack, the voltage will be increased from 10V to 12V after 5~10 minutes. When the battery reach >=12V, pre-charging stage is over and the charger will enter "Bulk charging stage".

Bulk charging Phase
    

This stage also called "main charge stage" or called " C.C." stage.

For Li-ion and LiFePo4 battery pack, the maximum C.C current should set as 0.2~0.5C. For NiMH and NiCd battery type, Bulk C.C can be set as 0.2C~1C; For Lead-Acid battery type, this C.C value should set between 0.1C to 0.2C.

Sample: For 12V 20Ah Lead-Acid battery, C.C should set as 2A ~ 4A

        For  24V 8Ah NiMh battery-pack, C.C can be set as 1.6A ~ 4A

        For  3s 2600mAh Li-ion battery-pack, C.C can be set as 0.5A ~ 1.3A

Trickle charging stage

    This name is just for NiMH and NiCd battery type. For Li-ion battery this stage should be called as "C.V"         stage rather than "Trickle stage".

For Li-ion and Li-polymer battery types, one cell C.V value is 4.20V,

for LiFePo4, one cell C.V. value should set as 3.65V

for 12V Lead-acid battery, this C.V. value is 14.4V

for NIMH and NICD, "trickle current" value is 0.02~0.05C.

Maintaining Stage

     This stage is necessary for Lead-Acid stage. For Li-ion. li-polymer and LiFePo4 battery types, this stage should be called "cut-off" stage. For NiMH and NiCd, this stage is merged with "Trickle stage" which I mentioned as above.For 12V Lead-Acid battery, the maintaining  voltage is set as 13.8V.