won't start and the battery will run down?

Hi when i start this car she may start first time, but some times after she has run for a time, she won't start and the battery will run down

We have changed the injectors but the problem is still there, she will start in the morning from cold but on occasion will not, its as if no fuel to injectors, this is the same when she has run, this is an intermittent problem, we are told it could be pump in tank, or high pressure pump

can you help
john