Battery charge current vs voltage?

Just to add a little more to the mix...
I have a bep dcm600 battery meter and great bit of kit it is too, gets used a lot. But I from experience I don´t trust the accuracy of state of charge from the amps in/out displayed. Also from the manual...

Charge efficiency
Charging Efficiency is set at 85% (factory default) ie the battery will only accept 85% of the charge current.
This is a difficult parameter to set as after 75% recharge the efficiency will fall off to 0% at full charge. The
overall efficiency will change with temperature, battery condition, charging current/voltage and discharge level.
Trial and error with general usage is the only way to find this efficiency.


And about Peukerts exponent...

NB: 0.01 change to Peukerts can make a reasonable change to calculated discharge. Alter in small steps.
For example, 100 Amps for 1 hour = 100Amp hours. Using Peukert’s exponent of 1.25, An x T, 1001.25*1=316
Amp hours. A 25% exponent change makes 316% change.
Calculating exponent “n” from discharge cycles is the only way to achieve an accurate discharge exponent.
This meter comes with a factory set exponent of 1.25, which is a “rough average for deep cycle flooded lead
acid.
If you do not wish to calculate “n” use the tables below to select a typical “n” for your battery type.
If after some time or use (6-12months) the accuracy seems to be degrading (possibly due to battery condition,
temperature, age – charging regime) it will be time to recalculate “n”.

I can´t see how you can rely on the accuracy of amps in/out to determin when a bank is charged. I have the "reset to 100%" set to less than 5a (200Ah bank) and 13.7v (from memory) for more than 5 minutes. Then if the fridge goes on the vlotage drops to below 13.7v and the unit won´t reset. Seems to work well.
 
Sybaris
1. True - otherwise you will sometimes get a false full reading which can increase over time. You are getting these from your description of plus amp readings.

2. False - you are not fully reliant on the shunt as when the battery is fully charged and then you start drawing amps the meter resets (page 20 in your manual - if you don't have a complete one here's the link http://www.xantrex.com/web/id/83/docserve.aspx

3. True But not 94. The default is A87 for your meter which is the default setting for flooded batteries (page 12). The only reason you are changing it is to disable the auto calc function. The actual adjustment from A87 to U88 is very small - much smaller than the errors a false full can and do lead to.

4. False You ALWAYS (not sometimes) have to put more in than you take out. What I wrote is a direct quote from your manual - page 19. It is false because the CEF is part of the meter and is used to calculate the difference between amps in and out - without this calculation no meter would ever be correct. The meter will not get increasingly out of sync because it uses this factor to calculate in real terms what is happening to the battery. In reality the meter measures in kw/hr and converts to amps for the reading.

5. True - Default is A87 for your meter (manual page 12). I would change it only slightly to U88 (U for user as opposed to A for auto) This is a very minor change and is only done because the meter will not recalculate. The CEF of a battery typically does not change for its life. (page 15 of the manual)

6. True

The amp counter is not just a shunt which is a non adjustable measuring device. The shunt measures amp either way and the meter's logic (algorithms) determine actual amps in by applying charge efficiency. In other words the shunt installed near your battery with the negative wire passing through it measures and the meter calculates the actual numbers using CEF. Your water example doesn't apply because it is just a flow meter while the Xantrex meter is a lot smarter, allowing for the inefficiencies of charging. It knows more than 1 amp has to be put in for each 1 taken out. While you may understand your meter better than before you still think it more like a flow meter. It is much better than that.

Remember you are getting plus amps on your meter. This is because of the problem we have been discussing at length. The meter as set (13.2v and 2%) calls the battery full when it is not. This means that when you draw your batteries down to an indicated 50% you are really less than that. This is cumulative. This kills batteries before their time. This is the entire reason for this change. Without this change the next time your meter shows 50% remaining it might really be 42% or some other number below 50%. This is one of the critical reasons to have a meter. If you go back to the water barrel and call it full when it may only be 90% full and then take half away you are now at 45%. You don't want to have this situation with your batteries.
Brian
 
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Conachair
"Charging efficiency is set at 85% (factory default) ie the battery will only accept 85% of the charge current."
A better way to say this is the wording Xantrex uses. Using their numbers which are slightly different from yours.
"The CEF has a factory default value of 87%. That means that the charger must return 1.15 AH to the system for the battery to restore 1 AH."
I think this is a bit easier to understand. CEF of a battery typically doesn't change over its life.
Puekert's exponent is known and most battery manufacturers (not necessarily rebranders though) publish it. The Xantrex manual lists it for popular battery manufacturers and it is different for each model of battery.
If your meter is set properly you can rely on the amps in/out for accuracy.
From what you state your settings are 13.7 volts and 2 1/2% (5 amps).
You state "Then if the fridge goes on the voltage drops to below 13.7 and the unit won't reset." The problem isn't the voltage which will not change as it is coming from the charger. It is the amps in to the battery that will change. Your meter will declare the batteries "full" when these 2 parameters (13.7 volts and less than 5 amps) are met for 5 minutes or more. But the meter only measures net amps. If your meter is on float charge (13.7v) and the amount of charge is 8 amps it will know that your batteries are not fully charged. But if your fridge turns on and uses 4 amps the meter will now only see a net of 4 amps going into the batteries. Because this is below the 5 amp setting, assuming the fridge is on for more than 5 minutes, the meter will call the batteries "full" when they have a ways to go. This is the problem and the reason the parameters are changed. Changing them stops the meter from being "tricked" into thinking the batteries are full when they are not. Because the meter knows charging efficiency relying on amps in/out is a lot more accurate than the false full reading.
Brian
 
Sybaris
Xantrex manuals are not the best written for easy understanding. While they don't say it in one simple sentence, they do say what effects the meter. But they say it in bits and pieces all over the manual. A full understanding of this makes it a lot clearer. Your meter is not "plug and play". To get the most out of it and accurate readings for your system and how you use it requires adjustments unique to you. If someone has no 12 volt loads when charging the factory settings should always be accurate. If there are 12 volt loads leading to a "false full" they won't be accurate as in your system. Just remember that when it reads 50% it could be quite a bit less than that.
Brian
 
reset

You state "Then if the fridge goes on the voltage drops to below 13.7 and the unit won't reset." The problem isn't the voltage which will not change as it is coming from the charger.

I understand your argument but it isn´t what happens. Maybe your charger is bigger than mine but I´ve watched the voltage drop as the fridge kicks in, I know it works, the meter will only reset when the amps in are low and the voltage is high for more than 5 minutes. Not convinced that peukerts exponant and cef will not change due to age and temperature either, most things do but I´m happy enough with the system so will leave it as it is.
 
Conachair
The meter reads "full" when the voltage drops not when it goes up. During charge voltage starts high and ends up at float level (13.7). It has to see a drop to float voltage and less than 5 amps to declare full. The voltage is not the big issue anyway, it's the amps in. When your fridge starts the net amps can drop below 5 and this combined with float voltage causes the meter to declare full when it still has a way to go.
Brian
 
Conachair,

You forget that Rich Stidger said it to be true, it doesn't matter what yours and my chargers actually do. There is also some confusion of if he said to lock the CEF to 94% or 88%, the way I read it http://c34.org/bbs/index.php/topic,4922.0.html it looks like 94% but I might need new glasses. It doesn't matter anyway because it is so close to 87% so the CEF value could just have been a fixed constant.

Also remember that the fact that when the charger is pushing in say 8 amps in acceptance mode and the fridge starts up, it may, just may, be smart enough to compensate for the draw of the fridge to keep the input at 8 amps regardless. Unless your charger is rated at 8 amps of course.

The way to go is to outsmart the logic of the Xantrex engineers. With a fixed CEF (regardless of what the efficiency of your batteries really is) and an estimated Peukert's exponent the amp counter must always be 100% correct so there is no need for any more logic. As Brian said, it does work.

Cheers,
Per
 
Can't resist joining in again!

I must disagree with Sybaris's point 6 and suspect normally meticulous mitiempo has misread what Sybaris is saying (unless I have of course).

Peukert's equation (or coefficient) is only used to predict how long the battery will support the discharge that is taking place at the time. It is not relevant to the recharge. If you take out 45Ah at 5A or 100A, it only relates to the same amount of chemical conversion and only requires the same amount of recharge, i.e. (45*CEF). The deliverable capacity to a given end voltage in a continuous heavy discharge is less than in a slow discharge because of transient characteristics in the battery, principally acid diffusion, and ohmic voltage drop. It is not because you have converted all the active material.

Where I still say all these systems are imprecise is because they all seem to take a single value for the CEF (and I don't see what else they could do). However CEF varies from near 100% below maybe 70% charge (unless you set the voltage high enough to gas) through 50% at near full charge to (by definition) 0% at full charge where it all goes as heat.

So a shallow discharge needs a lower CEF than a deep discharge. The nearer to full charge you are trying to get the battery, the bigger the inaccuracy. I imagine this is why the default definition of full charge in the Link system is actually quite a long way short of it. It makes the CEF variation less. (I note that part of the Link manual, about motorhomes, talks about treating 85% as fully charged).

As I read the manual - which I agree isn't the clearest in places - the Link does adapt the CEF on a historic basis but that will only work if all discharges are identical.
 
Willow
I agree the monitor is unable to vary CEF. While it does recalculate the CEF historically, it still does not (cannot) vary it in the middle of a charge cycle.

Regarding item 6. I did read it wrong. Now corrected. Sybaris understands Puekert. It means a 100 amp battery at the 5 amp rate will not give 100 amps at the much higher rate. But his understanding of the amount put back is off. When you draw the stated 45 amps the charger has to put back more - but the meter because of the CEF knows this and compensates. In other words the meter measures "real" amps going back in, which are really 45 x 1.15. If it did not compensate as best it could you would never be correct or even close in the meter reading.

I am not sure where you read 85% should be taken as charged. At one point in the manual (not sure where now) it explains that you use to 50% and recharge to 85% because if not on a shore charger the engine would have to run many hours to get the last 15% in.
Brian
 
Sybaris
He did say 94% for CEF. That is a big change for you in your system. If you have flooded batteries the proper setting (the default) is 87%. I'm not sure about what king of batteries Rich has but if he has AGM the number should be different (higher). You do have flooded batteries I believe. If you change it to 88% it will be fixed. That is why it is changed - off of A87 (A for automatic)

The charger is smart enough to compensate for the fridge draw, but that isn't the issue. It's the meter that will look at the net amps and say the battery is charged when it is not. We are changing this to get the meter more accurate, with no large plus amp reading (which we know has to be wrong). The charger will do its thing to completion and the meter should follow it, not jump to full prematurately.

There is nothing wrong with a fixed CEF as long as it is very close to accurate. The only reason we change the CEF is as stated to take off of automatic, where it recalculates every charge.
Brian
 
Err.. no disagreement with what you're saying Brian, but not sure we're tackling the same point.

Quote Sybaris:

The example of drawing 100Ah is obviously extreme but it shows that the amount put back will need to be more than that taken out if you are drawing more than 5 amps. True or False?

I took this to suggest that 45Ah taken out at 100A current would need more recharge than 45Ah taken out at less than 5A current. That's what is false. In either case it needs (45*CEF).

Apologies if I've misunderstood you Sybaris!
 
Willow
Sybaris is stating Puekert. Puekert as I said means that a 100 amp battery will give 100 amps at 5 amp rate but a lot less at 100 amp rate. This is true and Sybaris gets it. Then he gets a bit confused. He states that 45 amps out will need more than 45 amps back in. True. But the meter compensates for this (CEF) and the battery gets its 45 amps (x 1.15) which the meter reads as 45.
45 amps removed always needs 45 amps back in regardless of rate out. But the inefficiency has to be allowed for and the meter does this.
Brian
 
Willow
Sybaris is stating Peukert. Peukert as I said means that a 100 Ah (Ampere hour) (not amp as stated) battery will give 100 Ah at 5 amp discharge current i.e. 20 hour rate but a lot less at 100 amp discharge current. This is true and Sybaris gets it.
Yes!
Then he gets a bit confused. He states that 45 Ah out will need more than 45 Ah back in. True. But the meter compensates for this (CEF) and the battery gets its 45 Ah (x 1.15) which the meter reads as 45.
Yes!
45 Ah removed always needs 45 Ah back in regardless of rate out. But the inefficiency has to be allowed for and the meter does this.
Yes!
Brian

Just to avoid confusion of units which I know you understand yourself.
 
This is getting interesting and we are starting to get somewhere.

Willow3,
45 Ah removed always needs 45 Ah back in regardless of rate out. But the inefficiency has to be allowed for and the meter does this. Yes!
Well I am not sure, the way I understand it is that if I am drawing more than 5 amps from the battery I am getting increasingly less out of it. If I for example draw 5 amps I can carry on for 20h and hence get close to 100Ah before the battery is empty. If I instead in the extreme example draw 100 amps I can only do that for about half an hour, and will have only got 45Ah out of the battery before it is empty. Now to recharge a battery rated at 100Ah from totally empty (again an extreme example) I would always need to put in 100Ah. I.e. in example 2 the battery will not be full if I put only 45Ah back.

Now the Peukert value is an estimate and my interpretation right now (but I can change) is that 1.25 is an estimated average found for wet cell batteries, i.e. under normal conditions it has been found that if you for example sometimes draw 20 amps, and sometimes 3 amps etc. over time 1.25 seems to be a reasonable value in order to calculate the increased Ah needed to put back as opposed to that which was taken out.

BUT this clearly shows that the amp meter is only an ESTIMATE, but an estimate that we can of course strive to be as good as possible. What I have been trying to say in this thread (and I know you agree) is that I don't think disabling the Charged Parameters and the CEF value helps in getting a more precise amp metering.

Mitiempo,
The charger is smart enough to compensate for the fridge draw, but that isn't the issue. It's the meter that will look at the net amps and say the battery is charged when it is not. We are changing this to get the meter more accurate
Yes, now we agree. This is what I have been trying to argue all along. The meter cannot be perfect but we can try to get it as accurate as possible. Now my issue is that Rich was saying that his golf carts were being cheated of 10-20Ah. This is clearly wrong, the charger will charge the batteries correctly but the amp meter is out of sync. I do not however agree when you say that the meter is more accurate by disabling the Charged Parameters and the CEF.

Now regarding the CEF value. The factory setting might be A87%, but since it is A for automatic that is just a start value. Over time this will change as you cycle the batteries and the Charged Parameters are met. This is an intelligent way for the meter to try to be more precise. The Link 2000 manual indicates that the values don't change much over the lifetime of the batteries. Willow3 does not agree with this and neither do I. I think that this is based on an older manual because in my more recent Link 1000 manual they no longer say so, in fact, they point out that the CEF value will decrease as you keep cycling your batteries and when it gets lower you have a good indication to say that you need to equalize the batteries.

I have now also read the full Link 2000 manual (my manual is for the Link 1000) and I must say that it is much more detailed than my manual. We find clear instructions proving that the actual amp counter does not affect the charging (as opposed to Rich’s theory), and that in very bold print Xantrex does not advise you to disable the Charged Parameters and the CEF.

Here are some extracts:

Page 9. Setting the following parameters only affects the operation of the monitor, meaning that changing the Charged V parameter does not change the voltage set point of the charger in the Freedom Inverter/Charger. It only sets the point at which the monitor considers the battery full. Note also that when the Freedom is the charging source, the Charged% is always 2%.

Page 16. … This means that a maximum of 2.4Ah of overcharge would accumulate in a 24 hour period. [when in float charge] If your battery system is larger there will be proportionately more current flow and positive amp-hour accumulation.

Mitiempo: They actually say that some overcharge is normal on the meter, but that if the figure gets too large it might be for real and you might actually be overcharging the batteries. If you disable the system Xantrex designed to try to get a good amp reading as possible I think you are risking getting overcharged batteries without being able to monitor that to be the case.

Page 22. Rules for changing the Charged Battery Parameters. 1) The Charged Voltage MUST be at least 0.1 V BELOW the charging system voltage. 2) The Charged Current % times declared Battery Capacity MUST be GREATER than the minimum current the charging system maintains the battery at [a fixed 2% in the case of the Freedom charger as seen above]. If the charged parameters are not correctly selected, the LINK 2000 will never recalculate the CEF.

Remember, the 2% value was not taken out of thin air. In fact it is even hard coded into the Freedom chargers. It is by design meant to switch into float at that stage. My position is clear and I will not try to outsmart the Xantrex engineers by disabling my values. I also again have to repeat that this thread has been very useful and I now understand my battery system much better and am happy with the Status Quo.
 
Sybaris
If the Puekert value was set at 1 and the CEF was set at 1 you would have effectively a "dumb" meter with vast errors. This would be your "water gauge" taking into account absolutely nothing except flow in and out.
But you don't have this. You have a meter with a Puekert value of 1.25 which is the proper setting for flooded batteries. You don't seem to think this is very accurate. There is a solution to this. On page 24 of the Link 2000 manual it explains how by doing two discharge tests and a few calculations you can get an accurate value for your batteries. This requires a calculator with a log function. You can also do this using reserve minutes and the 20 hour rate. Alternatively you can look in the manual for your specific battery if it is Trojan, Rolls, or Surrette by model number. But this really isn't necessary. 1.25 is a midrange value for flooded batteries. It is based on the 20 hour rate and is plenty accurate for the kind of loads your battery will see. The uses that have a lot of problems with this are electric cars and the like where they use 100amp and larger loads which are quite extreme. I don't thing any boat would have this issue (unless you have electric propulsion!).

"I don't think disabling the Charged Parameters and the CEF value helps in getting a more precise amp matering."

We are not disabling them. We are changing the CEF by the smallest amount that we can only to get it to a manual setting instead of the automativ setting it is now on. There is still a CEF. It is not disabled.
The charged parameters are being changed so as not to get a "false full" reading. You must agree that it is bad for the life of the batteries to constantly drain them below 50%. If you get a false full reading and because you're drawing 12 volts for a fridge or whatever and the meter reset the batteries will start to drain before they are really fully charged. If the meter said "full" at a premature point, say 90% actual the meter would be wrong when you got down to an indicated 50%. It would be about 45%. If the same thing happened the next time it would add to the error. Not good for batteries. This cumulative error is much greater than any error possible by changing the CEF by a point. CEF is relatively stable and only changes a lot when the batteries are at end of life. But without correcting what the meter is telling you about your state of charge that is bound to happen a lot sooner in their life.

"Rich was saying that his golf carts were being cheated of 10-20 AH. This is clearly wrong, the charger will charge the batteries correctly but the amp meter is out of sync. I do however agree when you say that the meter is more accurate by disabling the Charged Parameters and the CEF." Correct! This is the problem. The batteries will charge but you will have a false reading - that is what we're trying to correct. When you are using batteries and want to be aware of their SOC you use the meter. There is no other way. And a correct meter will do the job better than an incorrect meter.

I don't know about the two different explanations of CEF, one saying it is stable and one saying it changes. I will look into that later.

Yes charged % is 2 on your charger. That is correct and is the float setting. No problem at all. We are changing it on the meter to avoid a false full not on the charger.

2.4 amp overcharge in 24 hours - a small amount. We're trying to avoid the false full which is potentially a much larger reading error (20-30 AH).

You cannot overcharge your batteries as the charger will operate properly. We're only changing the meter.

Page 22 We don't want the meter to change the CEF. That's why we are changing from A87 to U88. To get it off of the auto setting.

The 2% setting should be part of the charger's setting. No problem. This is the float setting and we're not talking about changing it. All we're doing is changing it on the meter to avoid a false full reading. Your batteries will charge normally. But the meter can trigger a full reading when both 13.2v and 2% is met for a period of minutes. As discussed this can be tricked by the fridge or whatever coming on at this time. We are not outsmarting the Xantrex engineers. We are not disabling values. We are changing then slightly to avoid you being misinformed about your batteries SOC. If the meter sees 13.2v and the NET charge current is 2% because of a fridge drawing the meter will say "full" at a much lower SOC than full. This is what we are trying to accomplish. Remember we're changing the meter, not the charger in any way.
Brian
 
Sybaris

Would you look again please at what I wrote earlier as I don't think I can really add to it and I think it answers the battery points you raise in your latest post.

I will add this though. You say that I said (in contradiction to mitiempo) that CEF will change over battery life. I'm not sure I did say that. In a good modern battery I'm sure it will change a bit but I don't think it will change much. What happens as the battery ages is that you lose capacity irrecoverably (chiefly because of sulphation or loss of active material). The recharge efficiency won't change a lot, you simply won't reach the capacity you had, no matter how hard you try to stuff electricity into it! In critical applications end of life is normally taken as 80% nominal capacity (incidentally nominal capacity doesn't mean that all the active material or all the acid are converted; it means how much capacity you get out to a standard (but arbitrary) final voltage in a standard time at a standard temperature). In everyday life people hang onto them much longer. It is true that in old design batteries CEF can degrade a lot over life, chiefly because of antimony (or other alloying agent) migration and deposition, but that should not happen in any modern battery because much lower alloying element concentrations are now used.

What I have pointed out is that CEF will change substantially with state of charge and at full charge is zero, which is why a battery on float will eventually start to show "overcharge" on any meter (well I guess there may be one out there clever enough to allow for it). There is still current but it's not harmful and typical float current will only be about 0.1% or less, not the 2%(?) at which the Link switches to float voltage.

I'm not going to comment on the Link meter queries as mitiempo clearly knows far more about the kit than I.

quote

Peukert's equation (or coefficient) is only used to predict how long the battery will support the discharge that is taking place at the time. It is not relevant to the recharge. If you take out 45Ah at 5A or 100A, it only relates to the same amount of chemical conversion and only requires the same amount of recharge, i.e. (45*CEF). The deliverable capacity to a given end voltage in a continuous heavy discharge is less than in a slow discharge because of transient characteristics in the battery, principally acid diffusion, and ohmic voltage drop. It is not because you have converted all the active material.

Think about your starting battery. When it's "flat" in terms of cranking, it will still light the lights won't it? Cranking actually takes little real capacity.

Where I still say all these systems are imprecise is because they all seem to take a single value for the CEF (and I don't see what else they could do). (You possibly could if you mapped instantaneous voltage and current to a look up table but is it worth it?) However CEF varies from near 100% below maybe 70% charge (unless you set the voltage high enough to gas) through 50% at near full charge to (by definition) 0% at full charge where it all goes as heat.

So a shallow discharge needs a lower CEF than a deep discharge. The nearer to full charge you are trying to get the battery, the bigger the inaccuracy.
 
Willow
Makes sense to me. The only points I'd like to make are:

1. While the CEF should vary during charge regardless of how the meter is set for this it is constant through the charge cycle, only recalculating at full if set on auto. I believe that it isn't a great issue however because if the battery does end up a bit less than charged the float charge will make up for it. If it's wrong the other way the battery won't accept it. Shouldn't be an issue as the current is low at this point.

2. You're right, float tapers off from 2% to a lot less as the battery finishes charge. We were concerned with 2% being the start of float and the meter calling it "full" when it had a way to go. Meters will show a slight overcharge but as the battery will not accept the excess it is not much of an issue.

Sybaris
The Xantrex meter only uses Peukert value for one item as far as the reading is concerned. As the discharge rate increases the available battery capacity decreases. Xantrex meters use the value for Time Remaining function only. This means that if you rapidly discharge the battery you will at some point see zero time remaining before you see the total number of amp hours used.
Brian
 
Summary

I have been spending enough time on this thread by now and after so many messages the arguments get sort of hidden behind the trees. For those of you still looking at this I will now make a summary of my take on this:

FACT: If you set the Charged Voltage above the float voltage, and the Charged Current % below that of the fixed charger value (2% in the case of the Freedom charger) as suggested by Rich and Mitiempo, then the Link logic that controls the automatic recalibration, and the the automatic CEF calculation, is disabled.
Source: Xantrex manual (Link 2000 page 22), and Rich.

FACT: Amp meters are not and cannot be totally correct over time without any recalibration (synchronization).
Source: Xantrex manual (Link 2000 page 20), and numerous discussions about Peukert and CEF estimates found in this thread

FACT: If you disable the Charged Parameters and want stop your amp meter from accumulating and increased error over time you will have to do a manual synchronization at intervals of your own choosing.
Source: Xantrex manual (Link 2000 page 20) and Basic logic.

FACT: The Charged Parameters have no influence on how the charger actually does charge the batteries, it is used only to calibrate the amp meter.
Source: Xantrex manual (Link 2000 page 9).

I made a comment earlier about the manual not being clear, that was based on my Link 1000 manual. Thanks to this thread I downloaded the Link 2000 which is very clear and informative.

This whole Freedom/Link discussion (at least as far as I am concerned) is about disabling the Link synchronization logic by setting the Charged Parameters to 15V 1% or not.

It is anyone's prerogative to opinion that the Xantrex logic is not smart enough, but I am not one of them, and nothing brought forward in this thread has convinced me otherwise.
 
Sorry you don't understand that the changes would give you a more accurate meter reading and probably extend the life of your batteries because if you take them down to 50% indicated it will very probably be a lot lower in reality. Remember that an early full reading will throw this off by a good margin. Any error you will get by disabling the Link synchronization logic is a lot smaller than this. It works well for myself and the people I have installed them for. Happy sailing.
Brian
 
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