[G2 and Desire Z Q&A, Help & Troubleshooting] kbeezie:
^This (regards to #1), and working batteries are rather cheap, the fat one I got (3500mAh) was 9$, but you can easily get a stock replacement of the 1300-1500 range to fit with the default battery cover.

Far as tips, rooted or not:

1) Screen to automatic, or avoid 'full brightness'. Your screen consumes the most of your battery, automatic or lower brightness can improve the life significantly. This is the big one as your screen will typically be 80-90% of your battery life.

2) If you are near wifi often, System Setting -> Wifi -> Advanced (via menu) -> Sleep profile to always on. This will set it so that the wifi connectivity is always on even with the screen off. A connected good wifi connection uses far less battery than your 2G/3G data constantly searching for a good or better data connectivity. Simply turn off wifi completely when not in an area with wifi (or if you're driving around).

3) Avoid unnecessary applications. Don't use twitter? Freeze/Disable the application under manage app or under Titanium Backup (generally it's not good to 'uninstall' an application completely if it came with the rom).

4) SetCPU with profiles is one way to do it, unless your rom comes with a CPU Daemon already (ie: mimicry with virtuous OC Daemon), When setting a "screen off" profile, try not to go below 768mhz for the maximum, as going with 384mhz for example may be too slow for the phone to effectively wake up when a call or notification comes in.

5) You can use an app such as Tasker (not to be confused with task killer). Where you can assign automatic tasks, such as automatically setting Radio to 2G when connected to wifi (some roms like AOKP do this automatically under power control), or other tasks depending on the circumstances.

6) The first time you get a new battery, make sure you leave it on the charger for a good 5-6 hours so that it accurately 'tops off', the phone won't know accurately what's 100% and what's 0% until it has been fully charged (least 6 hours minimum), and fully drained, after which it'll more accurately report your battery % as it's used and will have more accurate usage stats.

7) If you're a T-Mobile subscriber, consider the 26.13.04.19 radio as well as the T-Mobile Wifi calling app, wifi uses less power in the long run than your radio via cell towers. If you'll be in a location that has wifi often you will benefit from this over not using Wifi Calling. (The main downside is you cannot currently send/receive MMS over wifi calling, but Calls and SMS[txt] work fine). Even if you don't use the wifi calling app, the 26.13.04.19 radio provides better battery life over the older one.

---------- Post added at 10:53 AM ---------- Previous post was at 10:48 AM ----------

Course it helps to clear battery stats before performing this task so that the OS/Battery-Stats records the new maximum and minimum values of the battery. Though you don't need to do it monthly, I would say closer to 6 months would be appropiate if you don't want to make a monthly habit of it.

You mainly only do this on account of battery aging (over time the battery will not hold as much charge as it once did), You normally know if you need to do this task again if it appears to be on 98% or 99% forever never reaching 100%, meaning that the battery is no longer able to hold the juice to provide the former-maximum mV value, re-doing the battery stats simply makes the new maximum marked as 100%.

PS: Strip419, on an off-topic note, I tend not to 'thank' people who ask/beg for it. If your post is worthy of thanks, they'll be clicked on their own accord.