That charger is for an TRANSMITTER and uses a much higher voltage.

It is not suited for either a 4.8v or 6v RX pack.

A 4.8v pack wall wart type charger WILL charge a 6v pack, but not to absolute capacity. However it does get fairly close.

As mentioned it just takes longer.

Most wall chargers only output either 50mA or 100mA which is a conservative "trickle" charge for any larger pack.

I regularly charge 3800mAh 6v RX packs with a 50-100mA 4.8v charger.

I just don't get a full 3800mAh out of the batteries... normally I get around 3600mAh when charged this way, and that's just fine with me.

The s-l-o-w-w-w charge also assure the packs last much longer as it is very gentle on the chemicals.