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

Started 4 months ago | Discussions thread
OP jgveill New Member • Posts: 6
Re: LP-E6 vs LP-E6N vs LP-E6NH self discharge
1

Thanks Colin,

Sorry for the long post ... but I got results ...

Battery self discharge can be assessed in two ways : Open Circuit Voltage (OCV) and Potentiostatic Measurement. OCV is self explanatory but requires time (at least weeks) and a good DMM. Potentiostatic is done by injecting a very small current (10's micro amps) in a battery so that the battery voltage does not change.  The injected current is then the Self Discharge Current.  This can be done in 2 hours but requires very expensive equipment with many decimals for voltage and current. No need to say almost nobody other than battery manufactures are so equipped to qualify their batteries.  So, I have to rely on OCV but there are ways to get good results.

For OCV method, we first have to know that we cannot measure self discharge right after charging because other factors impacts voltage drop. After being charged, a battery must "relax" and it generally takes 8 days or less. Then, voltage drop should be coming only from self discharge current unless there's something else in the battery pack that takes energy, that's what I'm looking for.

I would not qualify Li Ion discharge curve as flat as we can see in the following curves. This are really typical Li Ion battery discharge curves.

3 - 3.2 v are the safe cut-off voltages. 2.5 v discharge voltage is playing with fire, as it can permanently damage batteries but it's generally how capacity is measured as shown here.

Temperature as well as SOC (State Of Charge) also affect self discharge. That's why you will see voltage going up with my 18650 batteries (4.091v after being 4.090v). As you mentioned the higher the temp, the higher the SOC, the higher Self discharge is. Few degrees around 25C does not change data too much on a longer period of time. To us, who do not have controlled environment, that means we have to wait more time to measure significant self discharge effects that surpasses temperature effects. Now my  8 days are over and I should soon be able to get a good idea on the Self Discharge Rate in the next days.

Here's the updated data for my batteries.

Li ion, typical 10-20 micro amps self discharge current does not drop voltage very rapidly.

With only 2 valid days, data does not look good at all for the newer Canon Battery packs. The 18650 stand alone Li Ion data has a very low drop.  Total drop (10days) as well as last 2 days drop makes sense. I will need much more time to measure self discharge rate for this battery.

The old NB-2L battery design already shows significant drop in the last 2 days.  That means high Self discharge or circuit taking energy. These are 10 years + old batteries and age could explain the result.

LP-6EN drop (total so far or last 2 days) is much higher than 18650. These batteries are almost new (200 pictures taken with these 2 batteries so far). Self discharge cannot explain such a voltage drop. Bad batteries or circuit taking energy.

LP-6ENH looks better than LP-6EN but is much worst than the old Canon battery design with the NB-2L.

So far, data shows that I will get stupid Self Discharge Current indicating that something else is discharging the batteries. The 2 last days drop demonstrates there's something else than Self Discharge current specially if you compare with the stand alone 18650. 10 times higher Self discharge current !

To get a real % power drop I have to have a curve like the ones shown before for each battery. To do, I will fully charge the battery and discharge it with 0.2C (for a 1800 mah this is 0.36 amp  discharge current) and store this data. With the data, and 2 voltages measurement some days apart, I will be able to compute the power % drop in that period of time.

I'm losing my time to compute this power drop. The drop I got so far with the last 2 days is way too high for Self Discharge Current only.  Storing the cells in the freezer could probably be the best thing to do to avoid Self Discharged Batteries but not for a circuit stealing energy from the battery.  I never had to consider doing this with the NB-2L and with the 20D batteries.

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