It's not too hard to design, as a computer controlled switchmode power supply. But it will be more expensive than just buying one of each kind of charger, and if you want to deliver 15V @10A (for charging the car battery) it will be quite bulky.
The key issue is that switchmode devices control output power by varying the pulse width. If you have 100% duty cycle corresponding to 150W (for the car battery) then the <1W for the AAA battery will be <1% duty cycle: a series of very narrow pulses widely spaced. That's bad for precision.
Then there's the safety issue. If you configure it for 12V @ 10A and plug it into the 1.2V AAA battery you'll have a nasty fire on your hands.
Charging just 3.6V (phone, 18650 cells) and Nicad/NiMH is a more reasonable prospect. Don't forget to build battery simulators for the three types before testing with actual batteries, so the inevitable bug in the design doesn't do damage.
Well I am not sure how much my answer will help you, but I am working on similar project of NiMH batery charging for last 2 months and putting what I have learned till date.
My confusion is about trickle charging the battery vs. fast charging it. I know that the trickle charging rate for a NiMH is between C/10 and C/40, which comes out to 245 mA and 61 mA, respectively, and fast charging is between C/2 and 1.2C
Trickle charge, as you said C/10, C/40 is usually very low charging current and is good for long battery life and mainly used in applications where you are not expected to the replace battery for months.
Fast charge is can be between C, C/2, 2C also and is used to revive the batteries quickly and come into action, but with this charging the battery life is reduced.
You can look into this link for specifics. So it depends on your application what sort charging you should go for. Tricke or Fast. And there is another term also called as Top-Off charge which is basically a maintenance charging.
My problem is finding an IC that can do both, specifically for NiMH batteries.
For fast charging we tested TI part BQ2002 which will only do fast charging and is good for 5V wall supply.Here is a 12V application circuit using BQ2002.
Then comes the trickle charging we tested BQ24400 and this IC controls the charging current based on the Rsense resistor and you can manually set the charging current based on your requirement.
I understand you are actually looking for a combination or merged properties of both the ICs I suggested, but if you are okay to go with some charging current between Fast and Trickle charging current, BQ2002 may be useful for you.
Now another important point is to take care for both the ICs is there charge qualification stage, they actually scan the battery voltage and temperature regularly before deciding which charging need to go. And when to terminate the charge, will again depend on the battery voltage and temperature of the battery. If you are not willing to use the thermistor for temperature sensing(like me) make sure to fool the ICs by providing the expected voltage on the Tsense pins to qualify for the charging. We have tested the fooling option it works fine.
And do not misunderstand me as TI agent, due to availability of free quick samples, we tested their parts as of now.
Best Answer
You might be able to use the NiCd charger to put charging current into the battery. It's the part where you "wait until finished" that the problem arises. The charge termination schemes (when to automatically stop charging) will be different. For lead-acid, probably switching from current-limit mode to voltage-limit mode at some maximum safe charging voltage. For NiCd/NiMH, watching the voltage for where it goes "over the hill" from increasing to decreasing, and/or the temperature rises quickly. Plus some other safety features, such as timeout, over/under-voltage, over/under-temperature, etc.
If you put the wrong chemistry on the charger it may never see what it's looking for to cease charging, because the battery behaves differently (voltage graphed over time has a different pattern). It could keep charging literally until the battery explodes. If you understand what the battery requires, and what the charger does, you might be able to use it anyway, to the extent you can manually observe and terminate charging as appropriate. You're risking destroying the battery, but in some cases getting a partial charge right now is more valuable than a longer lifespan later.
Your stated goal is measuring the capacity of the battery, rather than, say, getting enough charge back into your car battery so you can start the car and drive it around to finish recharging. If all you wanted to do was get "some" charge into the battery, considering you already know it's discharged, you could probably let it charge from your 2A source for "a while" and disconnect it manually after some time considerably less than (64A-hr/2A)=32hr, say 8-12 hours, watching with a voltmeter that the voltage doesn't exceed the maximum safe voltage and disconnecting early if it does. For your purposes of getting the battery fully charged and discharging to measure capacity, you'd want a proper charge termination scheme, which you don't have.