[Galaxy S I9000 Q&A, Help & Troubleshooting] wogfella:
Forgive the curtness of the email, am at work typing one handed while chowing down lunch :)

First point - you dropped your phone. I know that the new battery went okay for a while but is it possible that the phone itself may have been damaged?

Secondly, Email on Activesync over 3g will absolutely smash the hell out of your battery. Especially if you have push email going. Is it on push or is it set to check every so-and-so amount of time? Too short a period will kill the battery. The "Stock" email app that comes with Gingerbread 2.3.3 or lower seems to be just a big hog over push (for me at least). I also recommend changing the email "Amount To Sync" to a shorter number of days and set the amount of data to a lower value than stock (ie, "Headers Only" or 50k or something) so you download attachments on **your** terms.

Thirdly, you state you're in a poor reception area. This will most definitely affect the battery as the phone on a low signal or zero signal will waste battery trying to reconnect to the tower. Check your "Cell Standby" and see how muck time without connection you have. If it's anything above nothing, it's draining your battery. I recommend flashing a new modem (you'll need to investigate which one is good for your region/country/carrier) through ODIN (or Heimdall). Be careful when doing this and make sure you read up on the hows and what-to-do and what-not-to-do before you do - there is a (small) chance of you killing your phone and I do *not* want you to come back onto this thread and say it blew up (I want you to say "YAY THANKS WOGFELLA" :) ) Doing this voids your warranty so only do it if you either don't care or you really really want to fix your issue (and by default you don't care)

Fourthly, your wifi coming on and off - go to your Wifi settings, press your menu button and click ... advanced? Can't recall exactly (on ICS now). From there you can set your "Wifi Sleep Policy" to either "Never" or the other option that I can't recall. The default is set to turn the Wifi off when screen is off which of course means you lose your Wifi connection. **For your Email issue, try this first.**

Fifthly, your Wifi signal being weak in your display does not *always* equate to an actual poor connection. Sammy does many great things, but he does mess about a bit with icons and funny business. Check step four above and if you get bad Wifi reception when the phone is off (or while using it) then try messing about with your Router settings and also with the settings on your phone (take notes before doing so, I'm just throwing you ideas here....don't come back to me and ask me how to reset your router settings either!!!)

If that doesn't help then try flashing a custom kernel (kernel controls the Wifi). As above, doing this will void your warranty.

Sixthly, you say that everything was hunky dory and then went haywire. I reckon there may be an app doing funky things.

Try installing CPUSpy from the market and check to ensure your phone is going into decently long periods of "Deep Sleep"

Also, try installing the below app from this thread.

http://xdaforums.com/showthread.php?t=1179809

You're looking for high "Wakelocks" which will impact on your phone being awake instead of...well, asleep...when the screen goes off. Awake phone = cpu processing (even if it's not doing anything) = battery drain. Use Chamonix's recommendations on what is classed as a high amount of wakelock.

Facebook 1.7 for example, keeps the phone awake while checking notifications that just plain ain't there. For me, once I wiped this app, I regained about an extra 2-4 hours per day in use.

Seventhly, look over this thread:

http://xdaforums.com/showthread.php?t=939752

Has a heap of tips that helped me (before I got sick of stock Sammy and jumped to CM7 and then ICS)

Eighthly, and this is one that probably doesn't need to be said - cycle your battery and (controversial) bump charge. I mean, let the battery drain fully. Take the battery out for 5 mins. Put it back in and see if it turns on, and if it does repeat. Then fully charge to 100% and then unplug and plug back in. If your phone is already rooted then you can also wipe Battery Stats from Recovery.

Lastly - have you tried factory resetting your phone? It may wipe whatever it is that's making your phone freak out (if not the email) and you can start again. If you find that the battery goes bananas again after installing that app, you've found your issue.

So...to sum up:

Check your phone contacts.

Check your Wifi sleep policy.

Check your Email update rate.

Check the length of time you have the sync set for,

and the amount of data per email downloading.

Check to see if you are going into deep sleep.

Check to see if there are any apps holding wakelock (and bugger them off)

More extreme:

Factory reset.

Mess with your router settings if your wifi signal is still weak.

Very Extreme.

Flash Modem

Flash Kernel.

One thing not specified: What version Android are you running? SGS comes from Eclair up to (once Cyanogen and TeamHackSung get it rolling properly) Ice Cream Sandwich.

Hopefully *SOMETHING* in the above helps you.

Good luck!