Inspiron 1720 from sleep to hibernate at 75% battery

I am not sure whether this is normal: I usually put my laptop into Sleep mode after finishing work, so it's almost never turned off. However, it almost always goes to hibernation at about 77% to 75 % battery.

I thought this is must be set up in the Advanced Power Options of the Power Plan, and I checked that the critical battery level is at 10%.

So how can it be that it goes off to hibernation so early?

I have an Inspiron 1720, about a year old.

Thanks.

 

Vista?

In Vista go to control panel and power options click on change settings
then click on advanced
then sleep
then under sleep is hibernate, at times you have to set it here to make it work right,

this is another reason to upgrade to windows 7 the power settings work better, in Vista I had trouble keeping this working correctly at times.

 

Well, I have gone there and checked it.There is nothing in the settings that would imply going to sleep so early.

 

OK, I have looked through BIOS and all the settings I could think of, and found nothing that would implicate the behaviour.

Also, I have firmly verified it happens at around 78% of the battery, which is just weird.

 

What happens if you disable hibernation completely?