OK, guys, listen up.
You don't charge NiCd or NiMH batteries using any kind of reference to a voltage. Much like an LED, you care about the current going into the battery. If you're going to charge your battery manually, use a current-limited charger.
A fully-charged (or charging) NiCD or NiMH battery can be 1.4-1.5V. It quickly drops to 1.2V during discharge, and stays there for most of it's life. Thus, your 9.6V, 8-cell pack can read as high as 11-12V during or just after charging - almost exactly what you're seeing! Remarkable.
Most NiCd and NiMH batteries are perfectly happy being charged at a 3-hour rate (A-Hr rating / 3). Many are happy being charged at a 1 hour rate. Some are even happy being charged at 20 minute rates. It's all based on the way the manufacturer built the cell, and charging at too high a rate for the cell you have is a BAD THING.
OK, so let's assume you've chosen the 3-hr rate (600 ma in this example). How long should you charge? The simple answer is, until the battery starts to get warm. This length of time will vary based, of course, on how far discharged the battery is. What happens is that, while the battery is getting charged, most of the power going into the battery is fairly efficiently converting chemicals inside the battery from one state to another. There will be some heating due to resistance losses inside the battery, inefficiencies in the charging, etc., but the battery shouldn't rise more than, say, 10 degrees above ambient (depending on how well it's insulated, etc).
Once the battery is nearly fully charged, different chemical reactions start occurring inside the battery that cause most of the power being dumped into the battery to be converted to heat. The battery temperature will rapidly rise (think about it, at 12V and 600ma you're pumping 7 watts of power into a closed, fairly well insulated plastic box), and if the charging current isn't stopped, permanent damage to the battery will start occurring. This normally shows up as a significantly reduced operating time on the battery (your 1.8AH battery may become a 1.5AH, 1.0AH, or even 0.0AH battery!).
So, my suggestion is, if you're going to charge your battery by hooking it up to a power supply:
1. Set the current limit on the power supply to something reasonable (3-hour rate, say), and keep a finger on the battery. When it starts to get hot, shut off the power supply. If you walk away to go to dinner or something, plan on buying a new battery.
or
2. Set the current limit to something low (30-hour rate), and let it charge for a couple of days. NiCD batteries are generally specified to be able to handle a 30-hour charge rate indefinitely; they won't get damaged. NiMH batteries generally aren't - the manufacturers claim that any overcharge on a NiMH battery is a bad thing.
or
3. If you have profiled the battery you are planning to charge, you can set your power supply to the voltage that the pack reaches at full charge. Keep the current limit set to a c/3 or c/4 rate, and the current should naturally taper off as the battery approaches full charge. Unfortunately, you'll probably have to keep adjusting the endpoint voltage as your batteries age. What probably happened in this situation is the 12V you were cranking into the pack was close enough to the endpoint voltage that, by the time the pack was charged, the current going into the battery had dropped well below the 600 ma that you had seen early in the charging process.
Never use the cheap 10-hour chargers. They pump in too much current to leave the batteries on the charger indefinitely without damage, but don't have any intelligence to shut off the charger when the battery is full.
Never, ever think about charging a LiIon battery pack this way. Ever wonder why you can't buy AA LiIon rechargeable batteries down at Radio Shack? For liability reasons, the manufacturers of LiIon cells won't sell them except to manufacturers who show that they have designed-in circuitry to their product to keep the LiIon cells from being over-charged. If you attempt to charge a LiIon cell without the specific charging circuitry designed to protect the cell, you risk a right nasty little explosion.
And that's my opinion...
/frank