Battery Health

[oldhippydude]

Cheers I was under the impression that fully charged voltage would drop, along with mah..

That is my understanding too.
Clearly if a cell is holding less mah then the fully charged voltage has to be lower.

In deciding whether a cell has reached the end of its life, it is not just how much charge it is taking but how well it is holding on to the charge.
That is consistent with what I have heard Mooch say in a couple of his videos. I have never heard him put specific numbers on how much charge it should take and how well it should hold on to it.

In my test, after fully charging the cells I arranged them from best to worst then checked the voltage each day for four days. Two cells moved down the rankings on these daily tests. So it seems to me that fully charged voltage on its own is not enough to determine the health of a cell. It is also about how well it holds on to that charge.

My assumption is (please correct me if I am wrong anyone) is that a cell over time will hold less charge so will hold less mah so will not reach such a high voltage. A healthy cell will hold onto this lower voltage well but as the health of the cell deteriorates so does its ability to hold on to this charge when it sits unused.

 

[Andy S]

That is my understanding too.
Clearly if a cell is holding less mah then the fully charged voltage has to be lower.

Could you clarify? I'm not seeing why voltage and capacity would affect each other. The mAh is the amount of energy that's gone into the battery and the voltage is the force between the terminals. If the two were interdependent, then all new batteries with different mAh would also have different voltages but they're all 4.2 aren't they?

 

[nwhornet]

A battery will charge to 4.2v regardless of mAh but wont deliver voltage for as long on a worn battery. It will loose capacity quicker on a worn battery than a new one & hit cut off sooner.

 

[oldhippydude]

Could you clarify? I'm not seeing why voltage and capacity would affect each other. The mAh is the amount of energy that's gone into the battery and the voltage is the force between the terminals. If the two were interdependent, then all new batteries with different mAh would also have different voltages but they're all 4.2 aren't they?

Different cell chemistries mean different cell hold different mah.

As you charge a cell the amount of mah held by the cell increases as does the voltage. If you stop charging before the cell is fully charged then the voltage of the cell will be lower. If your older cells are can only hold a lower number of mah then they have to be reaching a lower fully charged voltage.
You seem to be claiming that your cells are holding less mah but still reaching the full 4.2v. Makes no sense to me.

 

[andipandi]

My older 25rs and vtc5a charge to around 4.18-4.20volts but once they've rested a while drop down to 4.10-4.14volts, lots of lag, it's the lag that makes me replace them, usually after 18 months, but that's too long really. Better off at 12 months, it's a money thing - and a gurning wife, that stops me. I'm currently rotating 10 pairs and 3 triple sets of 18650's, all due for replacement.

 

[Andy S]

Different cell chemistries mean different cell hold different mah.

As you charge a cell the amount of mah held by the cell increases as does the voltage. If you stop charging before the cell is fully charged then the voltage of the cell will be lower. If your older cells are can only hold a lower number of mah then they have to be reaching a lower fully charged voltage.
You seem to be claiming that your cells are holding less mah but still reaching the full 4.2v. Makes no sense to me.

What I'm claiming is what my charger is reporting. It stops when it reaches 4.2 and the mAh input gets a bit less each time I recharge. I don't see what chemistry has to do with it. I'm aware that it's the reason different batteries have different capacities but we're talking about how and why a particular battery loses capacity, not comparing batteries of different construction.

 

[oldhippydude]

What I'm claiming is what my charger is reporting. It stops when it reaches 4.2 and the mAh input gets a bit less each time I recharge. I don't see what chemistry has to do with it. I'm aware that it's the reason different batteries have different capacities but we're talking about how and why a particular battery loses capacity, not comparing batteries of different construction.

My nitecore chargers gives me none of the info your charger does. Jusa series of lights. i check voltage on a multimeter and have no easy way of testing mah beyond my subjective perception of how long a cell is lasting.

You are watching mah increasing as voltage increases. There is clearly a relationship. It therefore seems odd to me that as your cells age the are reaching the max 4.2v but holding less mah.

I suspect that if you tested your cells a little time after removing them from the charger like @andi52 has obviously done, then you would find that as they age they were not holding on to all of that voltage or mah for that matter.

 

[Andy S]

My nitecore chargers gives me none of the info your charger does. Jusa series of lights. i check voltage on a multimeter and have no easy way of testing mah beyond my subjective perception of how long a cell is lasting.

You are watching mah increasing as voltage increases. There is clearly a relationship. It therefore seems odd to me that as your cells age the are reaching the max 4.2v but holding less mah.

I suspect that if you tested your cells a little time after removing them from the charger like @andi52 has obviously done, then you would find that as they age they were not holding on to all of that voltage or mah for that matter.

While I acknowledge the logic of your position and don't know enough on the subject to counter it, one of my mods gives a reading on actual battery voltage, not just what's coming off the board, and when my charger says a battery is charged to 4.2 Volts, the mod agrees.

 

[nwhornet]

How do you explain the fact that a Sony VTC5A is 2600mAh & 4.2v charged & a Molicell P42A is 4200mAh & 4.2v. Other than two different sizes the only variable is the capacity, obviously more on the larger battery. If volts/mAh were dependant on each other the larger battery would have a higher voltage according to the thoughts expressed.
As a battery becomes worn capacity decreases to the point where it can't hold a charge, until then it will still charge tp 4.2v but wont deliver power for as long due to reduced mAh capacity.