Many years ago vehicles were fitted with what was called a dynamo, they would put out very little charge at idle and were very dependent on engine speed. They were generally replaced in the mid seventies by what we currently have, alternators, which are not dependent on engine speed to produce a continuous charge. [some manufacturers had them earlier, some later depending on the model of car]
The first check though is to ensure that the battery is in good condition, it's called a drop test, most garages will be able to perform this for you. Secondly, you need to be certain that the alternator is charging at between 13.75 [min] & 14.5 [max] volts.
If you are suffering from low battery charge at low speeds i would suggest fitting an ampmeter, you only need a temporary one to locate a problem, then with all your usual electrical items running, turn them off one at a time to isolate the drain. When you find the cause, check it out as an individual item, it may be faulty. Modern cars are designed to be able to cope with the demands of the systems fitted to them.