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Question on switching to LiFePO4 batteries.

Sterling1
Explorer
Explorer
I'm going to replace my 2 lead acid batteries in my Bigfoot truck camper with two 100ah LiFePO4 batteries. I've previously installed a 4 way battery selector switch to allow me to keep one of my batteries at a high enough charge level to start my generator (they are run in parallel). However, this won't be necessary (and probably won't work) with the lithium batteries and I will probably need to have it at the Both position to start my generator.

My question is is can I damage the batteries if I switch to the Both position when one battery is low and the other battery is fully charged?
35 REPLIES 35

StirCrazy
Nomad III
Nomad III
Sterling1 wrote:
StirCrazy wrote:

so, the plot thickens everything I find says 50% or higher and if you're not using them for a long time recharge every 3 to 6 months. I think this is another area where older chemistry myths might be carrying over

Yea, different manufacturers have different recommendations. I just wonder how much difference it makes in the real world.

For someone that really cycles the batteries a lot and is concerned about maximizing the cycle life it may make sense to take extra effort to store them in optimum conditions.

For someone like me who doesn't put a lot of cycles on the batteries storage conditions may not make much of a difference (as long as they aren't stored in a discharged state). They are more likely to die from old age than anything else.

It would just be nice to see how much of an impact storage SoC has on LiFePO4 battery life.


I try not to go by the manufactures but rather from the makers of the cells. What people call manufacturers in this area are really just assemblers. they don't make anything themselves; they just assemble off the shelf components. They may have custom cases made for them, or they might make custom solutions to hold everything together so there is a small possibility they might make a tiny part...

So, I tend to look at CATL, BYD, ELB and EVE cell manufactures, of which, the first three are the biggest in the game, and while EVE isn't as big they are known to be one of the highest quality cells on the market.
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

Sterling1
Explorer
Explorer
StirCrazy wrote:

so, the plot thickens everything I find says 50% or higher and if you're not using them for a long time recharge every 3 to 6 months. I think this is another area where older chemistry myths might be carrying over

Yea, different manufacturers have different recommendations. I just wonder how much difference it makes in the real world.

For someone that really cycles the batteries a lot and is concerned about maximizing the cycle life it may make sense to take extra effort to store them in optimum conditions.

For someone like me who doesn't put a lot of cycles on the batteries storage conditions may not make much of a difference (as long as they aren't stored in a discharged state). They are more likely to die from old age than anything else.

It would just be nice to see how much of an impact storage SoC has on LiFePO4 battery life.

3_tons
Explorer
Explorer
Sterling1 wrote:
….I understand that storing them not fully charged is best;

But I haven't found anywhere on the internet where it quantifies the degradation in life due to starting out storage in a fully charged state.


I could be wrong, but from a distance it seems to me like the answer in which you seek is embedded within your own question - just saying…

3 tons

StirCrazy
Nomad III
Nomad III
Sterling1 wrote:
I understand that storing them not fully charged is best. But I haven't found how much degradation it does to be stored in a fully charged state (but not connected to a charger). If it is a 10% degradation in life I I can live with it, but if it is a 50% degradation in life then I'd probably take the extra effort to discharge them for storage.

I haven't found anywhere on the internet where it quantifies the degradation in life due to starting out storage in a fully charged state.


I'll look at my literature for my cells and see if they say anything about how bad it is. like I said for short term I just keep it in my usage range as I run between 10% to 90% and never charge to 100% except the night before, or the day I am going camping I will go to a full charge and balance then reset my BMS to the regular operating range I use, but I am out almost every weekend (I work a 4 day on and 4 day off schedule) but when I am done with it for the winder I do drain it down to 50 to 70 which takes quite a bit. Usually, I just switch the fridge to 12V when I go to bed and then turn everything off the next day sometime. but I'll see if I can find anything that says how bad it is to leave them charged full.

so, the plot thickens everything I find says 50% or higher and if you're not using them for a long time recharge every 3 to 6 months. I think this is another area where older chemistry myths might be carrying over
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

Sterling1
Explorer
Explorer
I understand that storing them not fully charged is best. But I haven't found how much degradation it does to be stored in a fully charged state (but not connected to a charger). If it is a 10% degradation in life I I can live with it, but if it is a 50% degradation in life then I'd probably take the extra effort to discharge them for storage.

I haven't found anywhere on the internet where it quantifies the degradation in life due to starting out storage in a fully charged state.

StirCrazy
Nomad III
Nomad III
Sterling1 wrote:


I know LiFePO4 batteries should be stored around a 50% SoC for maximum life, but how important is this from a practical standpoint? I dry camp fewer than 10 times a year. If I were to give the batteries a full charge and disconnect them, top them off before going out, fully charge them when I returned (if they were significantly discharged), disconnect them and leave them that way for my next trip, how much am I really degrading their life? I realize I could boil some water in my microwave to get the charge level down but I wonder if it is really worth it.


I store mine anywhere between 70 and 90. It all depends on where they end up after my last night of camping, but that is during camping season. where I am camping every week or two. When the season comes to an end, I run my cell down to approximately 50% then turn the power off. with a 3% loss per month, I'll be fine till spring. you'll find everyone does things a little different.
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

Sterling1
Explorer
Explorer
A followup post and question.

I received the batteries with around 70% charge (13.2 volts). One of my concerns was if the batteries would be able to start my Onan Microlite 2500 generator (there was no surge rating for these batteries). My generator was able to be started with one battery so there should be no problems with two batteries in parallel.

I know LiFePO4 batteries should be stored around a 50% SoC for maximum life, but how important is this from a practical standpoint? I dry camp fewer than 10 times a year. If I were to give the batteries a full charge and disconnect them, top them off before going out, fully charge them when I returned (if they were significantly discharged), disconnect them and leave them that way for my next trip, how much am I really degrading their life? I realize I could boil some water in my microwave to get the charge level down but I wonder if it is really worth it.

StirCrazy
Nomad III
Nomad III
Sterling1 wrote:
StirCrazy wrote:

LiFePO4 is a different animal and while it has a few things you can't do like you did with your old fifty buck Walmart special, it isn't really that hard. little things like using a capacitor to preload your inverter circuit before you hook the batteries to it, on a new install, is it necessary probably not, but it does reduce the chance that feedback from a spark will take out any electronics.

even things like making sure you can parallel it, some can't, some have 2 battery restrictions some have 4. same goes for series installation, do the homework.

This is an interesting comment about the inverter. My inverter is currently connected directly to one of my batteries and doesn't go through the switch. I was planning on leaving it this way and see if I have a problem with parasitic draw drawing down the LFE battery when the switch is in the Off position. According to my inverter manual it doesn't draw any current when the inverter is switched off. If it did I was either going to disconnect it for storage or move it to the switch. I would hope the BMS can protect itself from the inverter inrush current. It is pretty common to have inverters connected to batteries and it seems like they would have precautions in the battery manual if it could harm the BMS.

My new LFE batteries are allowed to be connected in parralel but not series.


nothing to do with the inrush current, in your inverter the capacitors will stay charged when it is off for a long period. The reason from pre-charging the capacitors on a new installation is to prevent an arc while connecting them which could back feed. There is a more in-depth explanation than that, but I would have to go back and refresh my mind with it. Once it is hooked up there is no danger of this happening.

the point is not that though, the point was that there are several things we used to do with old battery tech that shouldn't be done with new. can you get away with doing a lot of it.. probably, but I don't want to be that one who finds out he didn't ..
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

Sterling1
Explorer
Explorer
3 tons wrote:
Best to just parallel the batteries, and assuming your inverter is less than about 4-5k watt's ( just ‘theoretical worries’…) you’ll find that inverter and BMS won’t much care…:R

3 tons

Thanks, my inverter is only 1500 watts.
Just to clarify, I plan to store my batteries with my 4 way switch in the Off position, so they won't be connected in parallel when stored. To keep them connected in parallel during storage I'd need to keep the switch set to Both (which would connect the batteries to the camper), rewire my switch, or put a jumper acros the positive terminals of the batteries. I'm hoping this isn't necessary.

3_tons
Explorer
Explorer
Best to just parallel the batteries, and assuming your inverter is less than about 4-5k watt's ( just ‘theoretical worries’…) you’ll find that inverter and BMS won’t much care…:R

3 tons

Sterling1
Explorer
Explorer
StirCrazy wrote:

LiFePO4 is a different animal and while it has a few things you can't do like you did with your old fifty buck Walmart special, it isn't really that hard. little things like using a capacitor to preload your inverter circuit before you hook the batteries to it, on a new install, is it necessary probably not, but it does reduce the chance that feedback from a spark will take out any electronics.

even things like making sure you can parallel it, some can't, some have 2 battery restrictions some have 4. same goes for series installation, do the homework.

This is an interesting comment about the inverter. My inverter is currently connected directly to one of my batteries and doesn't go through the switch. I was planning on leaving it this way and see if I have a problem with parasitic draw drawing down the LFE battery when the switch is in the Off position. According to my inverter manual it doesn't draw any current when the inverter is switched off. If it did I was either going to disconnect it for storage or move it to the switch. I would hope the BMS can protect itself from the inverter inrush current. It is pretty common to have inverters connected to batteries and it seems like they would have precautions in the battery manual if it could harm the BMS.

My new LFE batteries are allowed to be connected in parralel but not series.

mbloof
Explorer
Explorer
StirCrazy wrote:
mbloof wrote:
Sterling1 wrote:
I'm going to replace my 2 lead acid batteries in my Bigfoot truck camper with two 100ah LiFePO4 batteries. I've previously installed a 4 way battery selector switch to allow me to keep one of my batteries at a high enough charge level to start my generator (they are run in parallel). However, this won't be necessary (and probably won't work) with the lithium batteries and I will probably need to have it at the Both position to start my generator.

My question is is can I damage the batteries if I switch to the Both position when one battery is low and the other battery is fully charged?


In a word: No.

A battery is simply a energy storage device.

No matter what "type" or chemistry the batteries are if they have the same nominal voltage (IE: 12V) then the following would be true:

Battery #1 is 12.5V and Battery #2 is 13.5V and you hook them both together in parallel along with a load. What happens?

The load will draw current from BOTH batteries but since Battery #2 is at a higher charge voltage than battery #1 some of Battery #2's energy will flow to Battery #1 until such time BOTH batteries have the same charge voltage.

If you simply hooked a not-so-much charged battery up to a fully charged battery without a actual load the "not-so-much charged battery" would still be a load to the fully charged battery until such time that both batteries have equal voltage.

So can you can see the 'wasted' energy/charge being used for the lesser charged battery?

This is why it is generally recommended that to use two or more batteries in parallel they ought to be the same Brand+type+age+capacity and charge level so stored energy is not wasted charging the other batteries in the bank.


- Mark0.


You're forgetting about the BMS and the electronics in it.



It really does not matter.

Ether the batteries are at the same charge voltage or not. Period.

Don't over think it.



- Mark0.

Sterling1
Explorer
Explorer
mblof, hat you say makes sense for normal batteries. My concern is since LFP batteries have very low internal resistance they may be able to charge/discharge each other faster than what they can handle. Since my batteries only have a max 50 amp charge rate capacity I was concerned that the charged battery would try to charge the discharged battery so fast that it trips the 50 amp BMS limit (or worse - doesn't trip it) and then resets and starts the cycle over. It seems that constant tripping would be bad for the battery being charged (and perhaps the battery doing the charging).

I just don't know if this is a practical concern in the real world.

StirCrazy, I don't have autostart on my generator, this is a 2000 Bigfoot truck camper with an Onan Microlite 2500 propane generator. For some reason it wouldn't start when the batteries were low but starts fine with a fully charged battery. It would carank fine with low batteries but once it fired it would kick the starter motor out and faild to continue running. I gave up on trying to figure out what the problem was and put the 4 way switch in so I could reliably start the generator.

StirCrazy
Nomad III
Nomad III
Sterling1 wrote:
I'm going to replace my 2 lead acid batteries in my Bigfoot truck camper with two 100ah LiFePO4 batteries. I've previously installed a 4 way battery selector switch to allow me to keep one of my batteries at a high enough charge level to start my generator (they are run in parallel). However, this won't be necessary (and probably won't work) with the lithium batteries and I will probably need to have it at the Both position to start my generator.

My question is is can I damage the batteries if I switch to the Both position when one battery is low and the other battery is fully charged?


do you have an auto start on your generator where you can just adjust the voltage it starts at? Personally, I would just take the switch out all together or just replace it with an on/off switch. as for your shunt, as long as it is installed on the negative of the battery (right at the battery) it will measure the charge and discharge from the batteries no matter how you're charging it. will it pick up the genny supplying power to the camper, nope but to me that's not what's important, we use them to monitor the state of the battery, when you're running on a genny or shore power who cares how much power is going to your lights.

Steve
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

StirCrazy
Nomad III
Nomad III
mbloof wrote:
Sterling1 wrote:
I'm going to replace my 2 lead acid batteries in my Bigfoot truck camper with two 100ah LiFePO4 batteries. I've previously installed a 4 way battery selector switch to allow me to keep one of my batteries at a high enough charge level to start my generator (they are run in parallel). However, this won't be necessary (and probably won't work) with the lithium batteries and I will probably need to have it at the Both position to start my generator.

My question is is can I damage the batteries if I switch to the Both position when one battery is low and the other battery is fully charged?


In a word: No.

A battery is simply a energy storage device.

No matter what "type" or chemistry the batteries are if they have the same nominal voltage (IE: 12V) then the following would be true:

Battery #1 is 12.5V and Battery #2 is 13.5V and you hook them both together in parallel along with a load. What happens?

The load will draw current from BOTH batteries but since Battery #2 is at a higher charge voltage than battery #1 some of Battery #2's energy will flow to Battery #1 until such time BOTH batteries have the same charge voltage.

If you simply hooked a not-so-much charged battery up to a fully charged battery without a actual load the "not-so-much charged battery" would still be a load to the fully charged battery until such time that both batteries have equal voltage.

So can you can see the 'wasted' energy/charge being used for the lesser charged battery?

This is why it is generally recommended that to use two or more batteries in parallel they ought to be the same Brand+type+age+capacity and charge level so stored energy is not wasted charging the other batteries in the bank.


- Mark0.


You're forgetting about the BMS and the electronics in it.

The "best practice" recommendations are to fully charge each battery separately and then let them rest for 1/2 an hour. Then if the open terminal voltages are within 0.2V then it's good to hook them up.

LiFePO4 is a different animal and while it has a few things you can't do like you did with your old fifty buck Walmart special, it isn't really that hard. little things like using a capacitor to preload your inverter circuit before you hook the batteries to it, on a new install, is it necessary probably not, but it does reduce the chance that feedback from a spark will take out any electronics.

even things like making sure you can parallel it, some can't, some have 2 battery restrictions some have 4. same goes for series installation, do the homework. Also, while some do, it isn't recommended to mix LFP batteries of different types or different sizes. different brands may use different BMS units that may or may not play well with each other. in the case of different sizes, the smaller one will cycle deeply every cycle and wear out long before the other one.
2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100