Features:

• Small
  Batti takes very few space of your PDA memory. The battery indicator itself takes less than 20 KB and the whole application is less than 80 KB.
• Highly configurable
  Batti is highly configurable to suits your needs. You can set up the update interval of a indicator, its height, all colors are customizable and more.
• Hi-DPI aware
  Batti is designed in modern manners, it is ready for VGA displayes.
• Custom colors
  You can set colors for foreground and background, colors for low and critical level of your battery and you can set the color of indicator if your PDA is on AC power source.
• Detailed information
  Batti can show detailed information about your battery such as temperature, voltage, chemistry and some information about your backup battery as well.
• Charging
  Batti can indicate that your battery is charging. If you don't want this indication, you can easily turn it off.
• Battery levels
  In Batti, you can set up the value of low and critical level of your battery. Those two levels could be indicated with different colors (also configurable).
• Localizations
  From version 1.3, localizations are supported. You can make your own localization as well.
• Sound Events
  From version 1.4, you can set custom sound for entering low battery level, critical battery level, a sound for indicating the beginning of charging and a sound for notifying that your battery has been charged.
• Always On Top
  Batti can run as a topmost indicator, even if full screen applications are running.

More screenshots here.

Update Description:
v2.4 (01-09-2008):
- Fixed: Switched tab order in Settings on General page.
- Fixed: Redraw optimization (smaller CPU load).

v2.3 (18-07-2008):
- Fixed: Multiple Info dialogs when tapping on the indicator.
- Fixed: Tap on Adjust settings closes info dialog.
- Fixed: Correction coeficients are working again.
- Added: Support for AppToDate.

v2.2:
- Added: Gradient indicator.
- Removed: Icon from the top bar (some troubles on WM5+ devices), the icon can be activated in systray.
- Fixed: More gentle to battery.
- Fixed: Freezes when finished charging the battery.
- Fixed: Battery info is on the dialog, not in the bubble.
- Added: Preview for sound events.

v2.1:
- Added: percentage steps.
- Added: Correction coefficients for proper displaying of voltage and temperature.
- Added: Show icon in top bar.
- More WM5 friendly.
- Minor fixes.

v2.0:
- Added: automatic power-off on defined level.
- Added: Always On Top.
- Added: Configuration is displayed after installation.
- Battery info moved to notification area (bubble).
- Periodical update was useless due to the event detection, thus removed.
- Some code clean-ups.
- Minor bugfixes.

v1.4.1
- Fixed: Small bugfix related to localization (nothing critical).

v1.4:
- Added: Sound Events.
- Added: Option for turning off the frame around Batti.
- Added: Option for blinking on critical level.
- Added: Battery status on Info page (Charging, On AC, On Battery).
- Added: Custom color for charging.
- Some bugfixes.

v1.3:
- Added: Localizations.
- Added: Colors for low and critical state of battery.
- Added: Low and critical levels are configurable.
- Added: Action on tap.

v1.2:
- Added: Battery information.
- Added: Customizable color for situations, if PDA is on AC power.
- Added: Customizable left margin.
- Added: Customizable height of indicator.
- Added: Customizable update interval.
- Added: Charge indicator.
- Fixed: Support for Gigabar.

v1.1:
- Added: Config dialog.
- Fixed: icon for batti.
- Some minor bugfixes.
- Added: PPC2002 version.

v1.0:
- First public release.

SOURCE

http://code.google.com/p/batti/

Reviews:

**** [May 16, 2009] by Rick using Axim x51v Mobile 5
I like the idea-just a bar across the top. A small problem is that the proportion of the gradient colors doesn't match the battery status. When the battery is still at, say, 98%, the bar shows a lot of red and yellow. It looks like it is about 60%.

*** [Jul 29, 2008] by Saifuddin Jelly using DOPOD D600
Nice software, but dosen't sounds when the mobile is charged on standby mode and dosen't sounds when the battery if full when the mobile is in standby mode.

***** [Jul 10, 2008] by Jim using Sprint Mogul
Hands-down the *best* battery indicator out there. I like the new gradient, but wish I could set the start/end colors. Because the left-hand starts out red and I have it ending in white on the right, when I glance at my phone the red catches my eye and makes me anxious as I think I'm about out of power! Great program!

***** [Sep 18, 2007] by Matt using HTC P4530 (WM5.0)
Really like this program. Unfortunately, it seems to have an incompatibility with my synchronization software (OneBridge) which leads to occasional freezes.

**** [Jul 4, 2007] by Gunther using iPAQ 1940
Great little program, I've always wanted to be able to see my battery life without going into settings. Visually pleasing, and not as ugly as battery navigator, which just looks bad, and tends to cover up icons in my status bar. Batti looks nice and works nice, athough I would like the option to get rid of the big bar at the top and just have an icon in the status bar. also, I don't know if this is a big or what, but every time I choose to show the icon in the status bar, my status light blinks green nonstop, which is extremely annoying.

** [Jan 24, 2007] by A701 user using Mio A701 R65
I liked the configurability of this utility and used it for a few days. However when my PPC was recharging I had 2 lockups. The first time a soft reset recovered the problem. The second time I had to remove and replace the battery.

***** [Jan 17, 2007] by htc p3300 owner using htc p3300
Exactly what I was looking for! Don't want to fill up the today-screen unnecessarily. This does the job in very limted space, and has more possibilities for configuration than I could ask for!

** [Oct 9, 2006] by ppc6700 owner using Sprint ppc6700
Really like this utility. Seemed to work as described. Left phone in cradle & Sprint ppc6700 locked up. Could not unlock it & hard to do a hard reset. Hope authur can fix for next release.

***** [May 31, 2006] by Alexander Pochaev using HP hx4705 stock
Has all I need - always visible indicator 3 warning levels and auto shut off at critical level. And is very small. Great job author !!!

***** [Nov 9, 2005] by Glenn using Axim x51
Good. Very handy. I only wish I could turn off the frame border completly so I could set the height to 1 and still have the bar readable. Also I don't know if this is a bug but if I set the height to "0" I can't reopen the prefs, and the only way I knew to do that was to hold down the bar, so I had to reinstall. But very cool.

***** [Nov 9, 2005] by Burkay Genc using Axim X50
Small, functional, free... Don't miss it. An exceptional little tool.

***** [Nov 9, 2005] by Vinod Ponmanadiyil using O2 XDA II Mini
Wow... very responsive developer :) Can you Please incorporate an opton to disable this indicator for applications running in FullScreen mode? Thank you very much.

*** [Nov 9, 2005] by Lex using iPAQ 2215 WM2003
Doesn't display when Wisbar Advance 2 is in use.

***** [Nov 9, 2005] by Chester using Axim X50v
I love it! It's so simple and elegant and actually works. Some other battery indicators I've tried sometimes don't update.

**** [Oct 7, 2005] by Vinod Ponmanadiyil using O2 XDA II Mini
This is a Nice replacement for the spb pocketPlus battery indicator. An option to change the width of the Bar would be nice. Thanks.