how to determine current battery charge percentage.?

You really gotta do some peaking around, always depends on the battery and the pull of the charg that you are useing to charge with.... maybe below might give you a small ideal of something your looking for....I would spend hours on goog looking...Good Luck with your search...

This invention relates to battery charging methods and more specifically to

battery charging methods for lithium batteries.

Lithium battery cells have become increasingly popular for use in

electronic products. Lithium ion and lithium polymer technologies are

particularly useful for powering small portable electronic products, such

as radios, because of their lightweight and high energy density

characteristics. Unfortunately, lithium cells tend to take longer to fully

charge. For example, a 3.6 volt nominal, lithium ion cell being charged at

a rate of 1 C takes approximately two and a half hours to fully charge as

compared to a 1.2 volt nominal nickel metal hydride cell which takes

approximately one hour to reach 90 percent capacity. Customers of

rechargeable portable electronic products would prefer to have the

advantages of both a lightweight product and a reduced charge time.

Hence, it would be advantageous to have a charge system which would reduce

the charge time of a lithium battery.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a typical battery charging system.

FIG. 2 is a flowchart of a charging method in accordance with the present

invention.

FIGS. 3 and 4 show charging and discharging curves of a battery charged

using a prior art charging technique.

FIGS. 5 and 6 show charging and discharging curves for the same battery

charged in accordance with the present invention.

FIGS. 7 and 8 show one hour charge and one hour discharge curves for the

battery charged using the prior art charging technique.

FIGS. 9 and 10 show one hour charge and discharge curves for the same

battery charged in accordance with the charging technique of the present

invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While the specification concludes with claims defining the features of the

invention that are regarded as novel, it is believed that the invention

will be better understood from a consideration of the following

description in conjunction with the drawing figures, in which like

reference numerals are carried forward.

Referring now to FIG. 1, there is shown a prior art charging system 100.

System 100 includes a battery pack 102 and charger 112. Included within

the battery pack 102 are internal battery cells 104, an EPROM 106,

thermistor 108, as well as other possible charge circuitry 110 such as a

flex circuit, FETs, and polyswitches. A typical lithium ion charging

routine determines the voltage at which to charge the cell(s) 104 by

reading the EPROM 106. One problem with existing lithium charge ro tines

is that when the battery pack 102 is charged to the internal battery

cells' rated voltage threshold, the extra impedances in the battery pack,

caused by the charge circuitry 110, lower the effective voltage at which

the internal cell 104 is being charged. The charging routine to be

described herein compensates the voltage threshold to charge the entire

battery pack 102 by taking into account the impedance of the charge

circuitry 110 so that the battery pack can be charged to an optimized

battery pack voltage.

Referring now to FIG. 2, there is shown a flowchart representing a battery

charging method 200 in accordance with the present invention. Briefly, by

compensating the voltage threshold to charge the entire battery pack by

the product of the charge current and additional circuit impedance, the

battery pack can now be charged such that the internal battery cell

voltage is maintained at the rated voltage. The net effect is that the

internal cell can now be charged to its rated voltage and also that the

cell can now be charged faster.

The charging method begins at step 202 by storing the rated cell voltage

value (Vcell) and the rated minimum and maximum charge current values

(Imin, Imax), and characteristic battery circuitry impedance information

versus temperature for a given battery type into the memory, such as an

EPROM, of the battery. The battery pack temperature is measured by the

charger at step 204. The battery pack circuitry impedance is determined by

the charger at step 206 based on the measured temperature and the stored

impedance characteristics of step 202. This battery pack circuit impedance

includes, but is not limited to, such circuitry as the flex, FETs,

polyswitch, and any other associated impedances in the charge path but

does not include the battery's internal cell impedance.

Next, an optimum pack voltage threshold is determined at step 208 with the

following calculation:

The battery capacity that battery manufacturers print on a battery is the product of 20 hours multiplied by the maximum constant current that a new battery can supply for 20 hours at 68 F° (20 C°),[46] down to a predetermined terminal voltage per cell. A battery rated at 100 A·h will deliver 5 A over a 20 hour period at room temperature. However, if it is instead discharged at 50 A, it will run out of charge before the 2 hours as theoretically expected.[47]

For this reason, a battery capacity rating is always related to an expected discharge duration.

t = \frac Q I[48]

where

Q is the battery capacity (typically given in mA·h).

I is the current drawn from battery (mA).

t is the amount of time (in hours) that a battery can sustain.

I even have tried the two, aa rechargeables , and the xbox battery station. in my view I even have had greater success with the double aa rechargeables. The xbox battery packs look to lose the quantity of charge they carry over the years....so a ways as once you charge them, I constantly waited for the battery p.c.. to be empty. wish this allows

11.8 is 0% on an AGM.