uMBP battery life question

[brendu]

so ive had this 13"uMBP for a few months now and no way i ever get 7 hours. im not upset because it still outlasts all my friends laptops. My curiosity is that ive been web browsing for about 30 mins now, also iTunes is open but not running, and thats it. I checked my time remaining for the battery and it was 5h30m. 10 mins later it said 3h30m. 5 mins after that it now says 3h59m. What is causing it to jump all around like this? and is there a way to make it more accurate with its estimates?

also. I have calibrated my battery per the directions on apples website, did it about 5 days ago.

 

[Pau.c]

are you watching videos? or are you on flash websites?

 

[alecgold]

when the time machine kicks in, it uses a lot more juice.
Also several programs for indexing orso can take some serious capacity.
And last of the line, plugins in safari can serious take capacity on the CPU (10-15% isn't abnormal).
That can make a lot of difference.

 

[iBookG4user]

The battery life estimate is based on the amount of power the computer is using at that time. So if you were watching a movie the estimate would be lower than if you were using microsoft word or textedit. The screen brightness will also make a difference, so if you have the screen brightness changing due to the ambient light, it will effect the estimate.

 

[brendu]

no movies.. no flash, just browsing on macrumors at the time. Since the last post the comp has been closed, just opened it to check your responses, now were 89% and 4h38m...

 

[CJS7070]

I've found that on my MBP, the battery life varies from 3-6 hours, even when doing the same thing (like light web browsing, document editing, etc.) Usually it estimates around 4-5 hours, which is more than enough for me.

 

[SpaceKitty]

Anytime you so ANYTHING on the computer it will make the remaining battery time fluctuate. This includes opening a simple webpage, opening an app, emptying trash. Anything at all will cause it to fluctuate. Plus, you will never get 7 hours out of the battery unless you turn down the display to where it's barely lit, the keyboard lights off and just let the computer sit there not doing a thing.

I get about 5-5.5 hours on mine and I'm happy with that.

 

[fibrizo]

I noticed this too, so I did some testing, because I was going to take my laptop into the store to get fixed because I thought the battery life was bad.

So I tried as they said. 1/2 brightness, wifi on, bluetooth off, Keyboard light off and no devices connected. (All apps except safari closed)

If I clicked a non flash web page every 20 seconds or so, ie web browsing) My battery life was about 5:00-5:30. This obviously seemed totally wrong since they claimed 7 hours (which is still ludicrous it seems)

So I was upset, called apple, and they wanted me to bring it in to the store, after resetting pram etc. I thought they would think I was insane or maybe would swap it out so I swapped the original HD (160gb 5400 rpm) drive in and the original 2gb of ram in. At that moment it struck me, maybe that might make a difference. (I never thought it would really, since the seagate 7200rpm drive I had in it was supposedly very power efficient)

I booted back up and tried using it for a bit. Now my battery life was ~6:30. Which is closer to what apple says ( for some reason my battery health is 97% after 2 months and 13 cycles.)

So I plugged my 4gb of ram back in, and tried again, and ended up with about ~6:20. So I figured the power hog was my drive.

I then researched all the drives, and found the hitachi 500gb 5400rpm drive looked best in terms of numbers. (check other 5400 vs 7200 rpm thread)

I went and bought one, plugged it in and copied my stuff over from 7200 rpm drive and tested. I end up with ~6:15-6:30 if I use it lightly like apple says (ie no flash and clicking a new page 2-3 times a min)

However any real use (ie typing into a web page like I'm doing now cuts the usage time to closer to 5:45 or less) God forbid I use flash and my battery life is down to 4-4:30.

So to sum up, battery life according to apple of 7 hours is probably possible, if you end up browsing very little and letting your laptop sit there most of the time idle. Otherwise shorter battery life is normal, especially if you've upgraded the machine, or use it on more than 1/2 brightness, and key lights on etc etc.