Car died replaced battery died again after 2 days. Possible cause?

Low oil will not cause the issue you are describing..

You did not give many specifications about the car. If the car is old enough I think the problem is with the heater core, it's restricting the circulation.
The stalling problem, could the fuel pump or ignition problem. Do you have any error code?

If the motor gets hot and cuts off and will not start for a period of time the problem would be the crank sensor. The sudden cut off and starting right back up can be due to dirty battery cable connections. Remove them from battery and clean all three of them with a wire brush and replace both bolts.

have your battery checked at the local parts store. you might possible have bad cells in the battery.

I had the exact same problem with a chev where it would stall or almost stall at an intersection like it had a clutch, Mine seemed to only happen when it warmed up. It turned out to be the torque converter clutch (TCC) inside the tranny. Where my car was getting quite old I opted to just disconnect it, a local transmission shop confirmed it wouldn't cause any problems but I would loose gas milage on the highway. Where the 02 ranger is all electronic shifting you may want to check if disconecting would cause any problems.

I assume you have replaced the battery? If not have it tested.

Check to see if a glove box light, trunk light or under hood light is staying on. Also you can remove the negative battery cable and then reinstall it. When reinstalling it, if you see a spark (other than just a very small one) there is a current draw on the battery. This current draw can be isolated by pulling one fuse at a time to see when the battery stops sparking on reconnect. It is possible you could have a shorted voltage regulator causing the current draw also. Many things can cause this problem.

You have a bad battery, replace it

Your alternators should have a warranty on them...but if your car is breaking alternators, you may have the wrong size belt...maybe to small and putting to much strain on your alternator.

I would check that the auxilliary drive belt that runs the alternator and probably the water pump hasn't just broken, causing the engine to overheat and the battery to run flat. Just a suggestion, hope it helps.

If the alternator you installed was rebuilt, it may not have been right from the beginning.
There are high powered diodes used in them to rectify the alternating voltage produced to supply the DC the car needs.
These can fail quickly and without warning.
It is possible that a defective battery could cause this failure so a shorted battery could have caused both the original and replacement alternator to fail.
If you are in the US, you can visit about any of the chain auto parts stores and they will test your alternator free of charge but call first to check if your local store offers this.

If the regulator for the alternator is separate; some are, some aren't, this should also be tested if separate and is not that costly to replace.