Where are you getting this 14ma number from?
It's no secret that I HATE with a passion the current battery use/charging situation in these scanners. They should be using a LiOn battery pack and drop in charger, but I find it hard to believe the charge level is as low as 14ma's??
A drop in charger and direct-to-battery contacts as on a professional radio would be nice, but it would most likely cause a big jump in the price.
As far as internal charging current, it's a question of the capacity of the voltage regulator in the radio as well as the current requirements of the radio itself.
For safe overnight charging, NiMH cells prefer the c/10 rate, which for 2300mah cells works out to 230ma. I forget offhand what regulator GRE/Whistler use, but it's most likely a tiny surface mount device with little if anything in the way of a heat sink, and 230ma may be more than it could handle safely when combined with an operating radio.
That line of radios uses, if I recall correctly, a 9v wall wart for charging/operating. With a battery voltage of 6v and internal circuitry about the same, the regulator has to drop 3-4 volts at the needed current, which gets dissipated as heat. With no heat sink the regulator itself has to dissipate that heat; more charging current equals more heat, which would quickly fry the regulator.
So, they limit current to something that little bitty regulator can handle without getting too hot and self destructing; this probably means slightly more than a "float" charge. If the radio isn't being used for scanning at the same time, there could be more charging current available, but I suspect not as much as the c/10 rate.
There are a number of variables for current and voltage use they have to look at in the design process, but 14ma does seem low even for a float charge on 1000mah cells; even so I wouldn't expect much more than 30-40ma float as a trade-off between lower capacity and higher capacity cells if the regulator can handle it. I've seen somewhere that the default charging rate is somewhere around 200ma, but in reality I would suspect it to be lower, especially if the radio is in use and the cells are closer to being on a float charge.
Always better to charge the cells in a reliable external charger; better for them and better for the radio in the long run.