A few comments:
Is the ground on the computer spring loaded? If so any suitable metal would work for a DIY cable connector.
NiCd batteris can usually be resurrected to some extent. Sure, don't use batteris that have leaked or might leak if any leakage would eventually damage something. But if the battery is on the bottom you might continue using them. My method is to for a few seconds each time run loads of current into each short circuited cell, say like 5-10A or more. Eventually the short circuit goes away and it takes a charge. I usually charge it up to about 0.5V-1V with lots of current, and then I let a smart charger that can repeat charge-discharge cycles several times do it's magic on the cell.
For anyone not having a lab PSU suitable for this, you can use a halogen car headlight bulb (preferably the ones with combined low+high beam) in series with a car battery. The bulb will act as a current limiter and the low resistance for a cold gen bulb will actually just be good as it increases the initial current which seems to help getting rid of short circuits in NiCd cells.
Note though that the cells tend to go bad again if you don't use them really regularly.
Re the battery pin that turns on the red LED: Maybe the battery actually contains a temperature sensor, and it uses thermostat charging? That's a rather bad method as it causes extra wear on the batteries, but it was unfortunately how things were done back in the days. If you replace the batteries with something more modern you could use the output of a BMS connected to this pin to start charging if SOC is below a certain level, and stop charge if it's above a certain level. I would have some hysteresis so the charger don't switch on-off-on-off all the time (like so often that it might even cause radio interference and/or excessive wear on the cells).
I might be a scared chicken in this case, but I would never connect modern cells to any old school circuit. Sure, not likely but at least in theory someone might connect the car charger cable to a battery containing modern cells, and possibly over charge them with a car that can output >14V on it's 12V connectors. If you still use modern cells I would recommend putting a large label stating "never use car charging cable with laptop battery installed - fire danger" or something similar.
Is the ground on the computer spring loaded? If so any suitable metal would work for a DIY cable connector.
NiCd batteris can usually be resurrected to some extent. Sure, don't use batteris that have leaked or might leak if any leakage would eventually damage something. But if the battery is on the bottom you might continue using them. My method is to for a few seconds each time run loads of current into each short circuited cell, say like 5-10A or more. Eventually the short circuit goes away and it takes a charge. I usually charge it up to about 0.5V-1V with lots of current, and then I let a smart charger that can repeat charge-discharge cycles several times do it's magic on the cell.
For anyone not having a lab PSU suitable for this, you can use a halogen car headlight bulb (preferably the ones with combined low+high beam) in series with a car battery. The bulb will act as a current limiter and the low resistance for a cold gen bulb will actually just be good as it increases the initial current which seems to help getting rid of short circuits in NiCd cells.
Note though that the cells tend to go bad again if you don't use them really regularly.
Re the battery pin that turns on the red LED: Maybe the battery actually contains a temperature sensor, and it uses thermostat charging? That's a rather bad method as it causes extra wear on the batteries, but it was unfortunately how things were done back in the days. If you replace the batteries with something more modern you could use the output of a BMS connected to this pin to start charging if SOC is below a certain level, and stop charge if it's above a certain level. I would have some hysteresis so the charger don't switch on-off-on-off all the time (like so often that it might even cause radio interference and/or excessive wear on the cells).
I might be a scared chicken in this case, but I would never connect modern cells to any old school circuit. Sure, not likely but at least in theory someone might connect the car charger cable to a battery containing modern cells, and possibly over charge them with a car that can output >14V on it's 12V connectors. If you still use modern cells I would recommend putting a large label stating "never use car charging cable with laptop battery installed - fire danger" or something similar.
