how do i fix my sprinter?

brake fluid warning light comes on then battery warning light comes on then engine dies 20 mins later van starts no problem but brake fluid warning light stays on. you can then drive all day but eventually the battery light flashes and it starts all over again,had the one way clutch on the alternator changed still the same but if you rev past 4000 revs all lights go out then all is well until you turn off then it starts again any help would be appreciated thanks