LP-E6 vs LP-E6N vs LP-E6NH self discharge

Started 2 months ago | Discussions thread
Distinctly Average Senior Member • Posts: 1,206
Re: LP-E6 vs LP-E6N vs LP-E6NH self discharge
2

IR1234 wrote:

We don’t have any NHes but I can assure you all our batteries discharge at a fair rate of knots. Between two locations we probably have 50 LP-E6s and unless they are all used routinely they will discharge. And this happens to Canon and third party batteries.

But here’s the kicker, even if you think they aren’t discharged - they are! What happens is that the discharge internally does not seem to change the output voltage, which is mapped to discharge. So the battery internally is discharging, but when you reinsert the battery it initially registers a higher voltage than the one in the discharge map. So you think the battery is higher than it really is.

Over the next hour the voltage drops rapidly and you watch the bars disappear.

The winter is usually a big problem, we may not shoot for several weeks, when we get going again everyone is taking twice the number of spares to make sure they get through day, and then we start cycling through the batteries again. It can take 3-4 cycles before the battery fully recovers.

The chip in the cell doesn’t have a map. It is in fact quite a simple circuit. You are correct that the initial drop off can happen quite quickly as the voltage drops. The typical discharge curve shows that quite clearly where a cell charged to 4.2v rapidly drops to 3.7v which is the nominal voltage. In the LP-E6 packs there are two cells in series so effectively you can double that voltage and the respective drop. Also, due to the chemistry of these cells when they are fully charged the initial voltage will remain high even after a period of standing, but will drop off a lot faster.

So why do all batteries self discharge? There are a few reasons, chemical parasitic load and electrical load. As I am sure you are aware, there is a lot of energy in lithium cells compared to say an Eneloop type battery. The latter is unlikely to explode in your pocket or suffer massive thermal runaway. A lithium cell however, being highly energy dense requires protection against that. So in the pack is a circuit that protects against a number of things including over charging, discharging below a set threshold, over current protection, cell balancing, thermal protection. It is typically a chip that measures various parameters coupled with a mosfet used to disconnect the cells in the event of a problem. The most basic chips like the DW01 single cell protection IC continuously draws a very low current of about 50Na but that rises when in use. With multiple cells the protection draw when the pack is not in use draws noticeably more depending on the type of protection used. Over temperature protection for instance draws more than many expect. So some draw has to be taken into account there

We also have parasitic chemical discharge. When we charge a lithium ion cell the first 2hrs will see about 5% loss, after that they tend to draw ca4% a month. So after three months we can expect a minimum of 17% best case scenario. It goes further though. Temperature has a big effect on parasitic discharge with a high tem actually being worse. Temperature history has to be taken into account as that too changes the chemistry of the cathode. We also have internal shorts which are often very tiny but increase over usage again increasing parasitic discharge. There are huge white papers on the phenomenon so not worth boring people on here about it all.

What we can say is most lithium ion cells with good protection will loose around 25% of their capacity over three months, often more depending on the factors mentioned above. This is when the battery is not in the camera. If left in a camera drain will be faster depending on the camera and what features are left on. The GPS in the 7D2 was quite notorious for draining a batter even when the camera was off for instance.

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