How to know whether a battery is fully charged?

Hi everyone, I'm having problems in knowing when are the rechargeable batteries fully charged.
I had a battery charger system. Can anyone tell me what can i do to make the charger stop charging when its full.

What battery chemistry?

Excellent tutorials here.

NiCad/NiMH have a delta V characteristic where the voltage drops slightly once charged under constant current.

Li-Ion/Li-Polymer when the current drops to C/10 (generally) where C is the initial charge current based on the cell size when charged at constant voltage of 4.2v per cell under constant current.

Lead Acid are very similar to Li cells but at 2.2V-2.3V per cell.

caramelz said:

Hi everyone, I'm having problems in knowing when are the rechargeable batteries fully charged.
I had a battery charger system. Can anyone tell me what can i do to make the charger stop charging when its full.

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Can you provide the detail of battery charger system? It may not having end of charge detection.

For a new charger design, my suggestion is use uP based voltage slope detection technique.