i bought a hoover vacuum cleaner last week. it said charge for 6 hours but while charging the battery full indicator came on after 2 hours. i used the vacuum and got less than 10 mins. should have been 40 mins. so today i have replaced it with a vax vacuum. it says initial charge will take 4 hours. but after an hour and a half the battery full indicator is showing. do i still need to leave it plugged in for the full 4 hours anyway?