I'd like to add my 2 cents here since I've done a lot of research both into the 106 charging, had the infamous meltdown and also designed these types of battery chargers in the past.
Just to clarify, most LiIon AA batteries are rechargeable (not all), put out about 1.2 Volts DC, have a better discharge curve (voltage stability from charged to discharged), and require a very intelligent charger. The 106 will actually work down to just above 4 volts DC which means the radio will work pretty well on 4 LiIon cells which have about 4.8 - 5.0 volts.
What I believe you will find is that the LiIons will seem to last a much shorter time before recharge is required. What I'm saying here is that their much higher expense may not be a great deal for use in this application. And as others said here, Never ever try and charge LiIons in this unit. You are guaranteeing failure of the batteries and possibly the radio too.
In hopes to summarize all the great posts above and their recommendations:
1. Do not charge in this radio. If you need further evidence look at this post below I made a few months ago.
2. Know that putting any battery in the yellow holder and plugging in the adapter will put a charge voltage on it especially when the scanner is turned OFF. If you've made the mistake of putting Alkalines or even LiIon batteries in it you will destroy them in this case (and probably the radio too).
3. You can still have a potential destruction issue with the black holder as seen again from my post below.
If you want to have a couple of backup holders loaded with externally charged batteries, drop by RS or go to GRE site and order an additional black battery holder. Cheap insurance.
http://forums.radioreference.com/ra...55-pro-106-batteries-charger.html#post1451270