HTC Evo 4G - Battery FAQ

How to extend battery life

How to benchmark your battery and troubleshoot issues

How wifi drains batteries (tip: to save battery while using wi-fi, go into Settings, Wireless & networks, Wi-Fi settings, then press Menu, Advanced and set the Wi-Fi sleep policy to never)

Provider-refurbished batteries and how to avoid battery failure

Battery-Related Accessories: For information on various accessories including batteries, external battery packs and chargers, please read our List of Accessories and related discussions.

[Note: The information listed below in pink font is quoted from the source material listed.]

1) Do I need to prime or condition my battery?

A) No, Li-ion batteries do not need to be primed or conditioned like old nickle based batteries. ONE full drain and recharge is sufficient. (See also #2 below.)

Source: http://www.batteryuniversity.com/partone-12.htm

Preparing new lithium-ion for use

Unlike nickel and lead-based batteries, a new lithium-ion pack does not need cycling through charging and discharging. Priming will make little difference because the maximum capacity of lithium-ion is available right from the beginning. Neither does a full discharge improve the capacity of a faded pack. However, a full discharge/charge will reset the digital circuit of a 'smart' battery to improve the state-of-charge estimation.

2) Is it better to let the battery drain a lot before recharging it, or can I recharge it when the battery is only a little low.

A) Smaller recharges are better for battery longeviity than larger or full drains.

Source: http://www.batteryuniversity.com/partone-14A.htm

Should I use up all battery energy before charging?

No, it is better to recharge more often; avoid frequent full discharges.

Source: http://www.batteryuniversity.com/partone-16.htm

Manufacturers rate the lithium-ion battery at an 80% depth of discharge. Repeated full (100%) discharges would lower the specified cycle count. It is therefore recommended to charge lithium-ion more often rather than letting it discharge down too low. Periodic full discharges are not needed because lithium-ion is not affected by memory.

3) Is it ok to leave my battery plugged in, even if it is fully charged?

A) Yes, it won't hurt it as long as the battery doesn't overheat.

Source: http://www.batteryuniversity.com/partone-14A.htm
Should I remove the battery from the charger when full?

It does not matter. The charger automatically cuts the charge current when the battery is full. However, he also notes elsewhere: Limit the time at which the battery stays at 4.20/cell. Prolonged high voltage promotes corrosion, especially at elevated temperatures.[/i] (Caveat: See #4 below.)[/size]

4) I got a charger off of Ebay really cheap. Is it safe to use?

A) Possibly. I wouldn't leave it in after the full charge light goes on. Although I'm including the information below, the usual chargers off Ebay don't claim to be fast chargers. In fact, they tend to be extremely slow.

Source: http://www.batteryuniversity.com/partone-14A.htm

What should I know about chargers?

Charger should apply full charge. Avoid economy chargers that advertise one-hours charge. Fastest full-charge time: 2-3 hours.

5) My battery indicator says its full when its on the charger but when I take it off, it drops by X%. Is that normal? What is going on?

A) Yes, its normal. The battery indicator is an estimate of the state of the battery. If you'd like, you can remove it from the charger and then replace it. If the light turns orange, charge it again until the indicator goes green. Remember that, in addition to the information below, once the battery reads full, the safety circuit engages and shuts it off. After that, it will begin to slowly discharge.

Source: http://www.batteryuniversity.com/partone-12.htm

State-of-charge reading based on terminal voltage

The open circuit voltage can be used to estimate the battery state-of-charge of lithium, alkaline and lead-based batteries. Unfortunately, this method cannot be used for nickel-based packs.

On a lithium-ion cell, 3.8V/cell indicates a state-of-charge of about 50%. It must be noted that utilizing voltage as a fuel gauge function is inaccurate because cells made by different manufacturers produce a slightly different voltage profile. This is due to the electrochemistry of the electrodes and electrolyte. Temperature also affects the voltage. The higher the temperature, the lower the voltage will be.

ADDITIONAL SOURCE: http://www.batteryuniversity.com/partone-12.htm

The charge time of most chargers is about 3 hours. Smaller batteries used for cell phones can be charged at 1C; the larger 18650 cell used for laptops should be charged at 0.8C or less. The charge efficiency is 99.9% and the battery remains cool during charge. Full charge is attained after the voltage threshold has been reached and the current has dropped to 3% of the rated current or has leveled off.

6) I saw/bought some cheap batteries on Ebay. They come from Hong Kong. Are they safe to use?

A) I would urge extreme caution when buying off-brand batteries from Hong Kong. While they can be safe, they often are not, despite what the seller may say about it containing the requisite safety circuit.

SOURCE: http://www.batteryuniversity.com/partone-5B.htm

Asia produces many non-brand replacement batteries that are popular with cell phone users because of low price. Many of these batteries don't provide the same high safety standard as the main brand equivalent. A wise shopper spends a little more and replaces the battery with an approved model. Figure 1 shows a cell phone that was destroyed while charging in a car. The owner believes that a no-name pack caused the destruction.

Figure 2: A cell phone with a no-brand battery that vented with flame while charging in the back of a car.

To prevent the infiltration of unsafe packs on the market, most manufacturers sell lithium-ion cells only to approved battery pack assemblers. The inclusion of an approved safety circuit is part of the purchasing requirement. .. I would caution against using an unidentified lithium-ion battery from an Asian source, if such cells is available.

7) Which is better, Lithium-Ion or Lithium-Polymer?

A) I personally would recommend sticking with a Lithium-Ion battery. While you are hearing much in the way of Lithium-Polymer in advertisements (such as the iPhone) as though its a superior battery, in reality, it isn't.

SOURCE: The Li-Polymer battery: Substance or hype?

Unfortunately, the dry Li-polymer suffers from poor conductivity. The internal resistance is too high and cannot deliver the current bursts needed for modern communication devices and spinning up the hard drives of mobile computing equipment. Although heating the cell to 60°C (140°F) and higher increases the conductivity to acceptable levels. This requirement, however, is unsuitable for portable applications.

...

With gelled electrolyte added, what then is the difference between Li‑ion and Li‑ion polymer? Although the characteristics and performance of the two systems are very similar, the Li‑ion polymer is unique in that the solid electrolyte replaces the porous separator. The gelled electrolyte is simply added to enhance ion conductivity.

Technical difficulties and delays in volume manufacturing have deferred the introduction of the Li‑ion polymer battery. In addition, the promised superiority of the Li‑ion polymer has not yet been realized. No improvements in capacity gains are achieved — in fact, the capacity is slightly less than that of the standard Li‑ion battery. For the present, there is no cost advantage in using the Li‑ion polymer battery. The major reason for switching to the Li-ion polymer is form factor. It allows wafer-thin geometries, a style that is demanded by the highly competitive mobile phone industry. Figure 1 summarizes the advantages and limitations of the Li-ion polymer battery.

8 ) Who is this guy at batteryuniversity.com and why should I listen to him? What makes him such an expert?

A) Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC. Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decades. Award winning author of many articles and books on batteries, Mr. Buchmann has delivered technical papers around the world.

Cadex Electronics is a manufacturer of advanced battery chargers, battery analyzers and PC software. For product information please visit www.cadex.com.

Everything you wanted to know and more is available at www.batteryuniversity.com. The material is based on the book Batteries in a portable World - A handbook on rechargeable batteries for non-engineers, and is written in condensed form. The 300-page book and a library of battery articles are available on www.buchmann.ca. Battery service products are shown on www.cadex.com.

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