I can't complain I get pretty good overall battery life, although I would like to see what a replacement modded 2200-2500 battery would be like in this beast!
Every phone I've owned after my Treo 300 has been powered by a Lithium Polymer battery, and I've seen the same misconceptions and incomplete or bad information about those batteries in the forums for every one of those phones including the Evo. Well I'm home sick and can't do much else besides cough, so I'm going to try to educate y'all a little.
And why do I think I'm qualified to do that? Well I just turned 60 and I've been actively involved with electronics, both as a hobby and professionally, since I was 10. I've also been a model (R/C) aviator for many years and rechargable batteries have played a huge role in both of those pursuits. I began using LiPo cells in my projects and planes long before they started appearing in consumer electronics. Not much was known about them back then and we were basically on our own to figure out what worked and what didn't and we also had to design and build our own chargers. Those were exciting times given LiPo cells' tendency to "vent with flame" when they aren't happy.
So without getting too technical, here are some things you should know about LiPo battery packs:
The single most important thing you need to know is LiPo batteries can explode. They actually "vent with flame" with a big woosh, but "explode" seems to be the most popular description. Perhaps the surest and quickest way to make that happen is charge them beyond 4.2V per cell. Modern consumer electronics have plenty of built-in safeguards in place to prevent that from happening, but some "budget" battery packs and chargers don't have all the safeguards. The other common reasons LiPo packs explode is excessive heat and physical damage. I've personally seen two cars which had phones explode on the dashboard and it wasn't pretty. I also saw an executive's desk after a phone exploded in a drawer nearly 12 hours after he rolled over it with his car. The technical name for the phenomenon is "thermal runaway" and the actual chances of it happening to you are pretty slim if you stick to name brand batteries and chargers and use some common sense.
And you never want to forget or ignore this simple rule: If a battery pack ever starts to puff up like a little pillow or change size or shape in any other way, treat it like a firebomb with the timer ticking. Take it outside and put it in your barbecue or a steel pail or something.
While I'm on the "vent with flame" rant I'd like to add this: Almost all modern cell phones (including the Evo) use a single-cell (3.7V) battery pack. The charging circuit in the phone will prevent you from overcharging it, but all bets are off if you remove the pack from the phone and charge it in an external charger. One very common way model aviators accidently blow up LiPo packs is by charging them with a charger set to a higher cell count, and this could happen to a cell phone battery if you were to try to charge it with a charger made for a camera, for example. The other way model aviators blow up packs is by charging them at a higher current rating than they're designed for. I mention this because it may not be a good idea to charge a stock 1500mAh battery with an external charger designed for a 3000 mAh battery, but I can't say for sure without knowing the charging current of the charger. It would be both safe and acceptable to charge a 3000mAh battery with a charger designed for a 1500mAh battery, but it would take twice as long.
Next, you never want to discharge a LiPo cell below 3V per cell. 3V is completely discharged for a LiPo cell and if you go below that voltage you'll do unrecoverable damage to the cell chemistry. Once again, modern consumer electronics have plenty of built-in safeguards in place to prevent that from happening, but it's not hard to do by accident or by design once the battery is out of the device. Put the battery in an external charger and unplug it, for example ... No, don't.
There is no practical reason to unnecessarily discharge or cycle a LiPo pack. All you'll accomplish is reduce the number of charge-discharge cycles the pack will be capable of before it begins losing capacity. LiPo packs don't develop a "memory" like the old Ni-Cad cells did and they'll last significantly longer if subjected to partial charge-discharge cycles than they will with full charge-discharge cycles. In layman's terms, your battery will last longer if you charge it whenever you can rather than wait until you have to all the time. Also, the capacity of new LiPo pack will usually improve after it's been through a few charge-discharge cycles, but the best way to do that is through normal use.
LiPo cells have a shelf-life and they basically begin to degrade on the day they're assembled. But they degrade faster if they're stored at full charge, so if you won't use a battery pack for a significant length of time (~2 weeks or more), discharge it about half way before you store it. You don't need to get real technical about this because close counts. Just use the battery until the gauge shows about half green.
And finally this, for those of you who are compelled to play with volt meters:
A fully-charged healthy LiPo cell will have a resting voltage of 4.2V, but the nominal working voltage is only 3.7V. As I mentioned above, these cells are completely depleated when the resting voltage reaches 3.0V so the entire working voltage range for a LiPo cell is only 0.7V nominal. In low-current devices like a cell phone the actual working voltage range is more like 3.85V to 3V, but that additional 0.15V doesn't really amount to much. So what happens to that voltage range between 4.2 - 3.7V? In the simplest of terms, it's just a surface charge of sorts. Even at low current loads the voltage will quickly drop to the nominal working voltage where it will hold pretty close to steady until the cell is about 80% depleated.
The graph above is a typical 6C discharge voltage curve for an average LiPo cell. 6C means the cell was discharged at a rate (in mA) that was 6 times the rated capacity of the cell (in mAh). In other words, if the cell was a stock 1500mAh cell for the Evo, then the discharge rate would be 6 x 1500 or 9000mA (9A). Needless to say, a cell phone will only draw a tiny fraction of that current which would affect the curve in the following way: The starting voltage would be more like 4.1V and it would quickly drop to around 3.8V instead of 3.6V. Then the voltage would gradually drop until it hit about 3.4V and drop from there relatively quickly.
And that is just about everything you need to know to get along with Lithium Polymer battery packs and then some. To wrap this up, here's a short video of what can happen if you mistreat a LiPo battery. Judging by the visual evidence, my guess is it's a single 2100 to 2500mAh cell:
All well and good, but ours are li-ion in the one x
Quoted from another post here on XDA
Li-Ion & Li-Poly are the same thing
This Google search shows the One X has Li-poly battery, many of pages good info the One X using Lithium Polymer Battery type, so that is the info I'm using.
Specs here on XDA say its Battery: Standard battery, Lithium Polymer 1800 mAh
Processor: 1500 MHz NVIDIA Tegra 3 AP33H
Operating System: Google Android 4.0.3 (ICS) with HTC Sense 4.0
1024 MB RAM
Dimensions: 2.8 x 5.3 x 0.4 inches
Type: S-LCD 2 capacitive touchscreen, 16M colors
Size: 720x1280 pixels, 4.7 inches
Gorilla glass screen
Multi-touch input method
Bluetooth® 4.0 with EDR,A2DP,AVRCP
Wi-Fi®: IEEE 802.11 b/g/n
Micro USB Port
TV-out (via MHL A/V link, 1080p)
Camera: 8 megapixel color with autofocus, LED flash, 1080p recording, ImageSense Chip
Battery: Standard battery, Lithium Polymer 1800 mAh
GSM850, GSM900, GSM1800, GSM1900, UMTS850 (B5), UMTS900 (B8), UMTS1900 (B2), UMTS2100 (B1)
Data: GPRS, EDGE, UMTS, HSDPA, HSUPA, HSPA+
READ DOWN AT THE BOTTOM OF THE PAGE
Charging Lithium-ion Polymer
Charging Li‑ion polymer, also referred as Li-polymer, is very similar to a regular lithium-ion battery and no changes in algorithm are necessary. Most users won’t even know if their battery is Li‑ion or Li‑polymer. The word “polymer” has been used as promotional hype and does not reflect special attributes other than to know that the battery is built in a different way to a standard Li-ion.
Most polymer batteries are based on a hybrid architecture that is a cross between Li-ion and Li-polymer. There are many variations within the polymer family, and the true dry polymer battery for the consumer market is still years away. Also know as the “plastic battery,” this system was first announced in early 2000 but was never able to attain the conductivity needed for most applications at ambient temperatures. Read more about the Lithium-polymer battery and the Pouch Cell.
Simple Guidelines for Charging Lithium-based Batteries
A portable device should be turned off while charging. This allows the battery to reach the threshold voltage unhindered and reflects the correct saturation current responsible to terminate the charge. A parasitic load confuses the charger.
Charge at a moderate temperature. Do not charge below freezing.
Lithium-ion does not need to be fully charged; a partial charge is better.
Chargers use different methods for “ready” indication. The light signal may not always indicate a full charge.
Discontinue using charger and/or battery if the battery gets excessively warm.
Before prolonged storage, apply some charge to bring the pack to about half charge.
Over-discharged batteries can be “boosted” to life again. Discard pack if the voltage does not rise to a normal level within a minute while on boost.