Daz1712:
Hi.
By your discription i believe the battery packs you have are three cells (of 1.2 volts each) wired in SERIES no PARALLEL as if they were in parallel they would only be 1.2 volts.
The batteries are wired and then coated in heatshrink that protects the wires and holds them togeather so the CRACK may only be the outer heatshrink cover not the actual batteries.BEWARE when batteries have been sitting uncharged for a long time it is possable for one of the three cells to go flatter than the others. This can be a problem unless the charger is a very very good one.
Lets think of the batteries as water tanks, you have three tanks that you must fill full of water and you run a hose from your tap to each of the tanks.
When you turn the tap on to fill the tank you can only fill them so fast or the pressure builds and a tank goes boom. (Thats the current limiting)
There is a sensor on the tap that checks the preasure and when it goes up to high (as it would when the tank fully fills) it turns the tank off but this can only monitors the preasure of all three tanks at the same time so when the first one fills it turns off even if the others are not full.
This can happen when one tank has a slow leak and the others dont.When you use the water in the tanks there is a sensor that stops the drain when the first tank empties meaning you only get the capacity of the lowest tank.
The down side to having tanks in series.
The way to fix this is to fill each tank individualy or to put in a system that will allow water to trickle in at a preasure that will not explode the other tanks but will eventualy fill all the tanks.
If you dont believe the EXPLODING bit just try charging the batteries with no cutout.
The good chargers will monitor Voltage, Current and temperature of the battery pack and cut or modify the charge based on info from those sensors.
I would measure the voltage on the battery packs and see if they are at 3 volts or more. If not beware.
You will need a certain voltage to be able to charge the batteries and at a fixed current.
Oh perfect, yeah I thought the crack didn't mean much but the big all caps sealed label ticked me off a bit so I just had to be sure. Thanks for clearing it up.
Alright and now I understand with your water tank explanation that I have to be really careful with charging them too fast, thanks for that. I think I should probably get a more professional battery charger haha, but this is still just a little experiment with nothing to lose so I'll see.