# Thread: How do you test battery capacity?

1. ## How do you test battery capacity?

I have accumulated more than 10 BP-511 batteries over the course of my commitment to Canon.

The problem is some of them are hardly able to hold a charge anymore, but I can't work out which ones do and which ones don't.

What is the best way (apart from using each battery and firing away on the 20D) of finding out which are the best few batteries to bring on holiday, and which are the ones to throw away? I don't want to destroy my shutter just to save a few bucks on brand new batteries.

Any ideas would be appreciated.

2. ## Re: How do you test battery capacity?

use voltmeter..

3. ## Re: How do you test battery capacity?

I have a voltmeter, but how do you use that to test charging capacity? I mean how much charge it can hold from fully charged state to fully discharged state...

4. ## Re: How do you test battery capacity?

charge = capacitance x voltage [ Q = C x V]
charge = current x time [ Q = I x T ]

we either look at the effective capacitance of each battery..or the rootmeansquare current that passes through each battery during the charging/discharging cycle.

which one is better? or any other better measure?

5. ## Re: How do you test battery capacity?

I am guessing...
He is not worry about the amount of charge that it can hold, he is more worry about how long the charge can be hold. So, maybe, fully charge the battery, then use a multimeter to measure the voltage and current on day 1, then measure again on day 2, day 3, so on, until he sees a "significant" drop in voltage and current.

6. ## Re: How do you test battery capacity?

Erm, not really. I want to measure how much charge each battery can hold.

I've been testing the batteries by playing back an old tape on a Canon digicam that uses the BP-511. Guess what? The ones that I definitely will be throwing away are the original Canon ones. The Eastgear and Megapower ones are still pretty good. Interestingly some of them will cause a battery indicator to be displayed on the camcorder LCD, and some won't, so it seems there's some circuitry on the battery itself that reports the charge status.

The voltage on all of them is the same, though, so I don't understand how you can use the voltmeter. The current reading is off the scale, so that's no help.

Anyway, as long as the battery can playback more than half an hour I'll continue to use it.

Thanks.

7. ## Re: How do you test battery capacity?

You are actually trying to check if the BP511 is able to hold charge.

But there's a lot of parameters that are not known. 1) The discharge curve of the battery isn't linear. 2) The current drawn by the cam isn't specified. 3)The minimum operating voltage for the cam is not known...definately more than 5V.

But if you really want to try to DIY....

BP511 is rated at 1100mAh. This means it's supposed to deliver 1100mA for 1 hour.

You need a simple resistor to be connected across the + and - terminals of the batt.

Using V=IxR, where V=7.2, I=0.55 (50% of 1100mA to be on the safe side), thus R would be about 13Ohms. This would discharge your batt to 0V in 2hrs.

Lastly, NEVER discharge your rechargable batt to less than 30% charge unless you want to kill it quickly.

I use this

9. ## Re: How do you test battery capacity?

Originally Posted by CYRN
You are actually trying to check if the BP511 is able to hold charge.

But there's a lot of parameters that are not known. 1) The discharge curve of the battery isn't linear. 2) The current drawn by the cam isn't specified. 3)The minimum operating voltage for the cam is not known...definately more than 5V.

But if you really want to try to DIY....

BP511 is rated at 1100mAh. This means it's supposed to deliver 1100mA for 1 hour.

You need a simple resistor to be connected across the + and - terminals of the batt.

Using V=IxR, where V=7.2, I=0.55 (50% of 1100mA to be on the safe side), thus R would be about 13Ohms. This would discharge your batt to 0V in 2hrs.

Lastly, NEVER discharge your rechargable batt to less than 30% charge unless you want to kill it quickly.
Technique is workable. However, you'll need to get one of those high wattage ceramic resistor as well as a holder for the battery. The resistor will get hot so be careful.
And you need not discharge the fully charged battery for 2 hours, 0.5 to 1 hr would be enough. Repeat the test for all batteries and those with highest battery voltage after the test should be selected.

10. ## Re: How do you test battery capacity?

Originally Posted by Trojan
I use this
Is this available in Singapore ? Where can I get it ?

Thanks

11. ## Re: How do you test battery capacity?

there's nothing wrong with the formula,

Q (coulombs) = C (capacitance in Farads) x V (volts)

here, but i think this formula applies to capacitors and not batteries.

Originally Posted by user111
charge = capacitance x voltage [ Q = C x V]
charge = current x time [ Q = I x T ]

we either look at the effective capacitance of each battery..or the rootmeansquare current that passes through each battery during the charging/discharging cycle.

which one is better? or any other better measure?

12. ## Re: How do you test battery capacity?

tink all lithium-ion based batteries have some built-in circuit to cut off the battery supply if the voltage gets too low, hence protecting the battery from further damage....

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