Here's some data instead of hearsay...
In getting a plane ready for the conversion to the Spektrum DX-7 system I charged both batteries yesterday. The batteries are Electrodynamics 1500 mAh 5-cell 6v Ni-Cads. The chargers are standard Hitec wall warts showing 55 mA at 4.8 v for Rx and 10.8 v, also at 55 mA, for Tx on the labels.
The batteries were charged using the Rx side of the above chargers for 14 hours yesterday with the batteries removed from the chargers at 9:00 last night. I just took readings (under load) using an Electrodynamics digital meter
http://www.electrodynam.com/cgi-loca...205+1171822961 - 10 1/2 hours after removing the batteries from charge, and the voltages are 6.62 v and 6.63 v.
The above is consistent with my previous experiences... While it MAY take a bit longer to charge a 6 v battery pack with a charger nominally shown to be for 4.8 v batteries, it is not significantly longer, and nowhere near the extreme times (ranging from 'days' to '3 - 4 days longer') stated in other posts.
Get yourself a good digital voltmeter that will measure the battery under load and use that for your evaluations and confirmation of my data as well as before each and every flight.