Lithium batteries need a "battery management system" to prevent the charging current from going high enough to cause an explosive reaction from occurring.
The nicad and similar chargers don't have that and can cause battery fires or explosions. ~Bob~
Actually you *can* buy them on the internet, they are specialized items. But for regular consumer use, I'd say too many fires will happen. If you're concerned about self-discharge, try low-self discharge type NiMh. Eg. Sanyo Eneloop, Duracell Precharged, Rayovac Hybrid.
To the best of my knowledge there are no Li-ion AA or AAA batteries on the market. I have seen some rechargeable Li-ion batteries that are the approximate size of AA's but they are 3.7 volts and they require special Li-ion chargers.
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The nicad and similar chargers don't have that and can cause battery fires or explosions.
~Bob~