Archive for April, 2011

Canon NB-6L Compatible Battery Capacity

I have previously tested some of the electrical aspects of Canon NB-6L original and compatible batteries for my Canon PowerShot S95. These tests were sprung from a wish to minimise the risk of using a compatible battery. By comparing the electrical aspects I hoped to see if they were similar enough that I dared to use them in my camera! I am glad to say they were! I refer you to my previous post on NB-6L compatible batteries to read about the tests in more detail. (That test has now been updated to include the new Broadbattery battery mentioned below!) Maybe you will dare to try it as well? But remember that the risk is yours!

I was recommended a really low price and high-capacity (1600 mAh!) NB-6L compatible battery by one of my readers – thanks Francois! He found it on eBay at a shop called Broadbattery. Depending on where you live and how lucky you are in the bidding it can cost as little as $ 0.90 including shipping! (Which is a really super price!) I got mine for $2 + $2 shipping. It has just been delivered and I have now started the tests of this new battery – will update this article as soon as I have finished the tests – in a day or two!

As the selling point here was the high capacity I decided that just to measure the batteries under load was not enough – I needed a way to do battery capacity testing. Below you can see the results for all three batteries. Testing was done in a way as to simulate a real world picture taking.

For the technically curious

Arduino Battery Capacity Tester CircuitTo automate the test and to make it repeatable I came up with a small circuit controlled by a Arduino microcontroller  – you can see the UPDATED battery capacity tester circuit on the left. (If anyone is interested I can put up the Arduino program that controls it.)

Someone was! 🙂  (Interested in the Arduino program!) It outputs measurements to the serial monitor.  I just copy it from there to Excel and do the calculations and graphics in Excel.
See a separate post on this!

After some consideration about the measurement process I decided to try to approximate the real world picture-taking – but I also wanted a repeatable and reasonable easy and quick way of comparing different batteries. The circuit I decided on can handle the three most common batteries: 1.2 V NiMh, 3.7  and 7.4 V Li-ion by changing the load resistor. I wanted the load to mimic the actual taking of pictures by applying the load for a number of shorter times – like taking pictures.

For the 3.7 V Li-ion batteries on test here I decided that, as the battery according to Canon should give about 300 pictures, I would apply the load in around 300 short intervals. That ideally translated to a 5.2 ohm resistor giving around 500 mA load for 16 seconds each. Settled for a more standard resistor of 5.6 ohm. I also decided to let the battery “catch its breath”  for 16 seconds between each “picture” – again mimicking (very oversimplified) the real world behaviour while keeping the time down. Initially I wanted to follow a “real” standard like the CIPA one – but it was much to complicated for me and would involve far too much manual work. More to read about battery measurement in the CIPA document – but be warned it is very technical!

PEPs
This 16 second 5.6 ohm load followed by a 16 second rest period just had to have a name so I called it Photoman Equivalent Picture samples (PEPs) – cool eh? 😉 NOTE that this is not real pictures taken but gives a good enough approximation – especially for comparing batteries! . The circuit takes into account the resistance of the MOSFET transistor used – just below 0.4 ohm – but it lowers the load a little bit. Running through the whole test takes about 3 hours per battery. Cut off voltage is 3.0 V for Li-ion batteries so that is where I stopped the tests. (This goes well with my Canon S95 that signals empty battery at that voltage.)

mAh
My testing method also gives the capacity in mAh under the above “simulated real world picture-taking” conditions. Note that under other (“laboratory”) conditions these batteries can give other mAh capacities – but as I do it the same way in all my tests you can compare the results between the batteries that I test.

NOTE: As usual if anything goes wrong or gets broken by using this information I am sorry – but the all decisions are yours!

NOTE! New and improved Battery Tester at my Ar2uino Blog!

Capacity Test Results

To not get your (and my) hopes up too high I include an excerpt from a comment I made a few weeks back: After testing a few different batteries I am sorry to say that I strongly doubt that the capacity ratings given on these (and on most other cheap batteries) are much to go by – expect them instead to most often be around or slightly below the original battery. Most manufacturers seem to use the same (probably most cost effective) production – making them very similar in capacity”

That’s enough tech talk … now over to the result of the tests. I charged all batteries before the test and allowed them to rest for 10 min before starting the tests. This is what I got:

Rather typical Li-ion discharge curves – first a slowly sinking voltage and then an abrupt plunge! But the batteries looks quite different! Up to about 180 PEPs the curves keep very well together. A quick look at the discharge curves shows that the best performer is the Canon original battery.

Canon original
The curve shows an unusual stamina after about 280 PEPs working hard att keeping the voltage up. It is quite clear that the Canon original battery gave quite a lot more PEPs on one charge. Canon gave 352 PEPs and a capacity close to its claimed 1000 mAh by reaching 950 mAh(It also says “min 940 mAh” on the battery.)

Broadbattery – Unbranded
The curve starts out high – actually a little higher even than the original but when it reaches its limit then it plunges very quickly! Broadbattery came second with a very small margin (more like shared second place) with 288 PEPs and 780 mAh. This was after all a “small” disappointment as it promised 1600 mAh! Would have been nice with a really high capacity battery for the Canon S95. The battery should really be marked with “800 mAh” or something … (I have been in contact with the pleasant people at Broadbattery to see if it just is my sample – but I would not guess so… if so I will of course update this info!)

Deal Extreme – GodP
The curve is like a standard typical LI-ion curve from a textbook. The Deal Extreme battery gave 284 PEPsvery close to the Broadbattery. The Deal Extreme battery is marked with 850 mAh but did not quite reach that with 770 mAh

Conclusion 

It is definitely a difference between the three batteries – but is it worth the extra price and the risk..? That is something you have to decide for yourself… (Tip: I have bought a few compatibles…) I can still not say that I have a corresponding real world capacity figure – I seem to forget all the time and just change the batteries as they run flat. What seems quite clear is that you get a little less capacity for a lot less price!

An extra comment on the battery from Broadbattery is that apart from that they claim a much too high capacity – the battery seems to be very similar to the Deal Extreme one – so if you live somewhere to where they do free shipping and if you are a bit lucky at bidding  – this might still be a real bargain!

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