Do I need to disconnect battery to avoid charging/discharging cycle when plugged in?

[jjjggg]

I have Victron Multiplus and Battle Born batteries. The trailer is plugged into shore power. The float voltage is set to 13.5v. When Multiplus is in float mode and DC load is running, I noticed sometimes the power was pulled from the batteries and sometimes was pulled from the Multiplus and the Multiplus charged the batteries. My understanding is that when battery voltage is higher than float, it got pulled; when the battery voltage dropped below float, it got charged. Seems it’s in this cycle constantly when plugged in. Battery Born suggests I should avoid running load off the battery when plugged in but I don’t need to disconnect the battery if it’s multistage charger. Is it normal the batteries got charged/discharged cycle in float mode? Should I disconnect the battery when plugged in to avoid cycling the battery?

[rfequity1]

I dont have the Victron but I do have a BB lion battery. I too disconnect my batt when plugged shore power. My converter charges at 14.6 volts so once my batt is full charged, I dont want it to see that voltage for more than about 2 hours to balance the cells and then cut it off. So I have found best practices is to shutoff the batt when I arrive at a camp with shore power. It seems like if your setup is constantly charging then using your batts, then those cycles are counting against you for the longterm life of your batts. JMHO.

[dznf0g]

Originally Posted by jjjggg

I have Victron Multiplus and Battle Born batteries. The trailer is plugged into shore power. The float voltage is set to 13.5v. When Multiplus is in float mode and DC load is running, I noticed sometimes the power was pulled from the batteries and sometimes was pulled from the Multiplus and the Multiplus charged the batteries. My understanding is that when battery voltage is higher than float, it got pulled; when the battery voltage dropped below float, it got charged. Seems it’s in this cycle constantly when plugged in. Battery Born suggests I should avoid running load off the battery when plugged in but I don’t need to disconnect the battery if it’s multistage charger. Is it normal the batteries got charged/discharged cycle in float mode? Should I disconnect the battery when plugged in to avoid cycling the battery?

I am not completely sure of your description, nor am I familiar with the multiplus. But I am familiar with victron programming through the app. Does the multiplus have a setting for bulk voltage offset?

[richard5933]

If you disconnect you will totally disable the power assist function of the inverter. This is really helpful when you have someone forget that you are on 30-amp service and already have an a/c and a few other things running, and then decide to turn on the microwave. Instead of blowing the 30-amp breaker on the pedestal the Victron simply picks up the slack by pulling from the batteries.

Seems to me that having to manually disconnect the batteries every time you plug in defeats the idea of having an automated system which should be trouble free. Find the setting in the Victron menus to get the system set up to function the way you want it to. If you can't find the setting on the basic menu, it might be on the one you access with the laptop. Contact Victron for specifics if you need - I've found they are very helpful.

[CMHM]

Battleborn recommends batteries not to be plugged in for more then 3 weeks at a time. So you can always unplug for a day each week. Fully unplugging the batteries defeats the point as someone else said.

[jjjggg]

I didn't change the bulk offset. I believe it's 0.2v by default. Also I found the float voltage is not constant. It's up and down between 13.6~ 13.3~ looks like a sine

[fran&frank]

Your Multiplus is a inverter-charger and doesn't provide DC power directly to your DC circuits like a converter-charger does, it provides power to the battery and the battery powers your DC circuits. If you disconnect your battery you will not have 12 VDC power even when on shore power with the Multiplus on, and if you turn the Multiplus off it will not pass AC power through to the AC circuits. The kind of shallow cycling you are describing doesn't hurt your lithium batteries but keeping them charging at a full state of charge for long periods of time can. So when using your trailer keep the Multiplus on and the batteries connected but when not using your trailer it is a good idea to turn the Multiplus off and disconnect the batteries to eliminate parasitic drains on your batteries. Setting your float voltage at the natural resting voltage of your batteries is also a good idea, often around 13.4 volts. --Frank

[Kevinshortnh]

The Multiplus is connected directly to the batteries, so it will continue to charge (or maintain charge) them even if you "disconnect" the batteries with the "Use vs Store" button. The "Use vs Store" switch only disconnects the loads that use the batteries - with a few exceptions, per some deviations in wiring between models and anything connected directly into the front battery compartment.

[Wazbro]

Does the Multiplus even work without the batteries connected?

The inverter-charger on my mothers trailer wont let AC pass through, supply 12v or charge the batteries if the batteries are below a certain voltage or not connected.

[jjjggg]

I got a response from Victron. I was told that it's normal and after turning off both DC and AC load, both the voltage and current are very steady. So, false alarm! Here's the response from Victron

"Looks normal if you have any loads attached. You are reading the battery voltage reacting to draws and charging. The Multi will have a very stable voltage. Turn off all of your loads – AC and DC and see what happens."

[mikeinca]

My understanding is that, in general, lithium batteries don't like to constantly be held at 100% charge. (There is plenty of information about this to be found on the web.) For example, the manufacturers of both of our EV's recommend that for longest life the lithium battery packs should be charged to 80% capacity for daily use and be fully charged only when anticipating a long trip. This is also true for lithium cell phone batteries which will retain their useful life longer if not constantly charged all the way.

I'm not sure from the OP's post whether his question relates to a storage situation or when he is travelling. When travelling I typically want full batteries, so whether charging from the solar controller or using the Victron Multiplus when hooked up to shore power at a way stop, I allow them to charge to 100% and then float. This is typically a relatively short-term situation, so I don't worry about it too much.

But when storing long-term at home I let the BattleBorns charge to around 80% (in my case using solar) then "unplug" and allow the batteries to discharge slowly with the residual drain from the trailer. When they get down to around 50% (which usually takes a couple of weeks) I start the charging process to 80% again.

My Multiplus allows me to choose either a charging function, an inverting function, both or neither (off). If the OP just needs 12V he can turn the Multiplus off. If he needs 120V he can activate the inverter function when plugged into shore power (that's the only way my setup will supply 120V). And if his batteries need a charge he can, of course, activate either the charge function or the combo charge and inverter setting. Just don't leave the BattleBorns on charge all the time, would be my advice.

[dznf0g]

Again, I am not familiar with rv applications of lithium, but do the available BMSes allow 100% charges???? My ev BMS will not allow either full charge nor full empty states. There is a buffer at both ends. You are correct, neither should be allowed with lithium batts.
Edit: for example, my volt has a 18.4kW battery. Only 14.1kW is usable.

[mikeinca]

Originally Posted by dznf0g

Again, I am not familiar with rv applications of lithium, but do the available BMSes allow 100% charges???? My ev BMS will not allow either full charge nor full empty states. There is a buffer at both ends. You are correct, neither should be allowed with lithium batts.
Edit: for example, my volt has a 18.4kW battery. Only 14.1kW is usable.

You're correct, and what you say is applicable with respect to our EV's too. One has a 95kW battery of which 86kW is "useable" while the other has 93.4kW of which 84kW is useable. Despite this built-in buffer, the manufacturers of both vehicles recommend daily routine charging only to 80% to extend battery life.

It's possible that the BattleBorn RV lithium batteries also have an overhead buffer built in since their rated spec (for the ones I have) is shown as 100Ah of "useable capacity" and the BMS will certainly keep them from being overcharged. This type of overhead may, in fact, be typical of most lithium battery applications, including cell phone batteries. Even so, if one googles the subject, one can find ample information that the charging sweet spot for long life of lithium batteries is around 80% with constant "full" charging being detrimental to longevity.

Maybe I'm being overly cautious, but since there is no reason to routinely keep my RV batteries at full charge I choose not to do so, just in case.

[dznf0g]

Originally Posted by mikeinca

You're correct, and what you say is applicable with respect to our EV's too. One has a 95kW battery of which 86kW is "useable" while the other has 93.4kW of which 84kW is useable. Despite this built-in buffer, the manufacturers of both vehicles recommend daily routine charging only to 80% to extend battery life.

It's possible that the BattleBorn RV lithium batteries also have an overhead buffer built in since their rated spec (for the ones I have) is shown as 100Ah of "useable capacity" and the BMS will certainly keep them from being overcharged. This type of overhead may, in fact, be typical of most lithium battery applications, including cell phone batteries. Even so, if one googles the subject, one can find ample information that the charging sweet spot for long life of lithium batteries is around 80% with constant "full" charging being detrimental to longevity.

Maybe I'm being overly cautious, but since there is no reason to routinely keep my RV batteries at full charge I choose not to do so, just in case.

I do wonder if some are indeed being overly cautious. In my OEM training, there was never a mention of the need for more than the 80% rule. In fact, the Gen 1 batteries were 20% at the top and 20% at the bottom. Gen 2 Batts were only about 12% at both ends. The only mention of any deviation, was if you were going to store the car for more than 2 weeks, you should run it down to below the useable top (ie, 80% on the range gauge) and leave it unplugged. I had between 7 and 8 years fleet experience with the Volt and had Zero comments of reduced range over time.

My Volt is 3.5 years old, and 40k on the odo, and it still has 14.1kW of range. So I wonder if this message has been convoluted over time on the web.

It is true that some MFRs of cars did NOT engineer a buffer and suffered the consequences. (as well as not providing liquid cooling).

So, this begs to question....does anyone have info on the various RV lithiums relative to the BMS charge routine? Do any of the Victron devices have a programmable battery cutoff feature. I know the Smart Battery Protect has a cutoff for the lower end....for LA batts, but Lithiums behave differently and a simple voltage cutoff probably isn't sufficient. I don't think it has an upper end cutoff provision.

[richard5933]

Originally Posted by mikeinca

You're correct, and what you say is applicable with respect to our EV's too. One has a 95kW battery of which 86kW is "useable" while the other has 93.4kW of which 84kW is useable. Despite this built-in buffer, the manufacturers of both vehicles recommend daily routine charging only to 80% to extend battery life.

It's possible that the BattleBorn RV lithium batteries also have an overhead buffer built in since their rated spec (for the ones I have) is shown as 100Ah of "useable capacity" and the BMS will certainly keep them from being overcharged. This type of overhead may, in fact, be typical of most lithium battery applications, including cell phone batteries. Even so, if one googles the subject, one can find ample information that the charging sweet spot for long life of lithium batteries is around 80% with constant "full" charging being detrimental to longevity.

Maybe I'm being overly cautious, but since there is no reason to routinely keep my RV batteries at full charge I choose not to do so, just in case.

This is all good, and I'm sure that there are specific methods of charging which can squeeze a few more cycles out of the batteries.

To me though, it all needs to be balanced against the purpose of having them - to be able to enjoy using the trailer. There is only so much futzing with something like this before I'll be met with a comment that goes something like this, "You spend more time with those batteries than you do with me!"

Part of finding that sweet spot is getting the system setup so that the automated charging parameters can take care of nearly all the needed adjustments, and you're left to simply enjoy using the trailer.

I haven't made the switch to lithium but in our coach I do have the Victron system with the Multiplus II. I'm wondering if deep inside the advanced settings found when accessing through a laptop if there isn't a way to set the charge parameters to accomplish what you've described automatically.

[dznf0g]

Yeah, I'm not on lithium yet either. I upgraded to agm just last year. Waiting for all this kind of stuff to get sorted out. The agm switch has driven some hardware updates, and I am buying all victron, with lithium capabilities.
This bms stuff is at the heart of my concerns though.
Does anyone have details on their brands of batts?

[GettinAway]

Oh boy.. Mine have been plugged in to a 30 amp outlet at the farm for the last 12 months. (Except when traveling). I had no idea leaving them on would cause damage. Agh!

[dznf0g]

Originally Posted by GettinAway

Oh boy.. Mine have been plugged in to a 30 amp outlet at the farm for the last 12 months. (Except when traveling). I had no idea leaving them on would cause damage. Agh!

Maybe, and maybe not. This is why I ask these questions. Some manufacturers may have taken this into account. Some may not.
I do think, until you know, you should run them down to at least 90% and leav.them disconnected from all parasitic loads. Every few months, charge them back to less than full. IF, and only if internal battery temps make it possible/advisable.

That is another question. I know that most bms do not allow charging below a.certain temp, but what about high internal temps? They shouldn't be charged nor used above 90* (or so) cell temps, by my training.

[wulfraat]

Originally Posted by fran&frank;

Your Multiplus is a inverter-charger and doesn't provide DC power directly to your DC circuits like a converter-charger does, it provides power to the battery and the battery powers your DC circuits. If you disconnect your battery you will not have 12 VDC power even when on shore power with the Multiplus on, and if you turn the Multiplus off it will not pass AC power through to the AC circuits. The kind of shallow cycling you are describing doesn't hurt your lithium batteries but keeping them charging at a full state of charge for long periods of time can. So when using your trailer keep the Multiplus on and the batteries connected but when not using your trailer it is a good idea to turn the Multiplus off and disconnect the batteries to eliminate parasitic drains on your batteries. Setting your float voltage at the natural resting voltage of your batteries is also a good idea, often around 13.4 volts. --Frank

This is correct. The multi is not a converter and must always be connected to batteries to function while on shore power. It is not optional.

Floating lithiums is not the best for their health. What I do is turn off charging for the multi, and let the batteries supply dc power on their own. I’ll let them get down to 50% then turn charging back on. This avoids float.

These batteries will last 10-20 years, I have no concerns about cycling them.

[thewarden]

Originally Posted by mikeinca

But when storing long-term at home I let the BattleBorns charge to around 80% (in my case using solar) then "unplug" and allow the batteries to discharge slowly with the residual drain from the trailer. When they get down to around 50% (which usually takes a couple of weeks) I start the charging process to 80% again.

Cycling your batteries like this when in long-term storage will also shorten the lifespan of your BBs. They have a finite number of charge/discharge cycles. While that is in the many thousands, why waste them at all?

When I long term store my trailer, I charge the BBs to about 80-90% and then disconnect them. After many months of storage, they pretty much have the same change in them as when I disconnected them.