It'll be the battery; pretty much guaranteed. If the battery is knackered, and the pump can't draw enough charge, it'll turn off. If you then unplug the battery and plug it back in, it'll work for a few minutes, then cut out.
It'll work on setting 1 because it won't draw much power, but anything above that, it'll cut out after a short time.
You just need to try a new battery before you do anything else.