That depends on your setup like how many widgets are you using, do you have live wallpaper on etc. An indication that you may need to bump charge your battery is when all of a sudden you feel that the battery life gets shorter even though you're using your phone normally. Let's say that you normally get 1.5 day, out of the blue it dropped to 0.5 day. Your battery then either needs to be recalibrated or it is physically damaged. A total recalibration would be to discharge the battery totally, partial charge, wipe the battery stats and recharge it to full power. But that would need a root permission or some crazy looking adb commands (at least to those outside the Linux world), so HTC came up with this bump charging method that is more suitable for all users (with or without rooted device).

Anyways, EVO 4G is an awesome phone but with a terrible battery life (as reported by its users). Here's a post detailing how to fix it. There are probably some tips in there that may apply to other HTC sets:-
http://www.cloudave.com/link/fixing-the-ba...-evo-incredible

Another unproven myth is that task killers can improve battery life. This has been debated in countless occasions. Do task killers really help? Or is it just a placebo effect? Does it do more harm than good? Here are some good threads on the issue, read them if you have the time and you decide:-
http://androinica.com/2010/05/07/google-an...-are-pointless/
http://www.google.com/support/forum/p/andr...87bb09cba&hl=en
http://forum.xda-developers.com/showthread.php?t=683176
http://forum.legendroid.com/android-genera...-on-your-phone/

I used task killer on my 1.5 Hero. It did help in releasing memory and maybe prolonging the battery life a bit. But since going to 2.1, I didnt see any difference using a task killer in terms of battery life. In fact, on Eclair, I found that my phone was lagging whenever I have the task killer on. So, I abandoned it. On FroYo, task killer is made more redundant as FroYo's memory management is just fantastic. You'll get twice as much free memory than on Eclair.

I assume you're in Recovery. Did you mount the filesystem?  

ummm... yes. you can ls the directory to reconfirm. 
Actually the safe way to do it is to mv the file to some other place and later if things get screwed up, you can always un-mv the step. But WTH. 

yup. if there .bin file wasnt there and you try to rm it, you'll get an error message. An echo would mean that the command was successful.

BTW when I wrote about how to manually wipe the battery stats, I was doing it hypothetically. I wasnt expecting someone would actually attempt it. 

If you charge it during off state and it straight away go green, it is at full capacity. Anyways, if you want a more detailed report on how your battery is faring, go to the Market and look for 'OS Monitor'. If you go to the 'Misc' tab you'll see some info about the battery. If you see 4000mV and you're around 90% capacity or more. Then the battery is fine, generally speaking.

Here's the good part though, something that can measure whether bump charging will have any effect on your batt. Go to the 'Message' tab and click the 'menu' button on your phone. Choose 'Option' from the pop-up menu and scroll down until you see the 'Message' section. In the 'View Log' option choose 'dmesg'. Tap 'Filter dmesg', check 'Enable Filtering', tap 'Tag Filter' and type 'batt' in the text box. Get out from the 'Options' (press 'back' a couple of times) to the 'Message' tab. You'll now see a more detailed stats of the battery condition, including the rate of it discharging. Apply some common sense here, a Desire/Nexus battery is 1400mA (it's actually more but HTC rounds the figure). So if your condition is at 100% and you see the reading is below 1400mAh (like 1300mAh or something worse), then you'll need to bump charge it and reset the battery stats as it is obviously giving the wrong reading. Some guys on XDA managed to get it up to 1480mAh through bump charging. That mAh is actually an indicator on how much juice your battery has. The more, the better.

nope!
i type batt

all i see is funny numbers
batt:ds2784_notify:1 36 at 93348742377249

batt: batt:power_supply_changed: battery at 933487504337890

What kernel are you using for that ROM? is it a .32? 
Can you do this through ABD? :-
adb shell
? dmesg | grep -i batt

Please show me the output.