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Old 10-01-2022, 09:56 AM   #1
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Living up to the hype Lithium Batteries

Moving to LiFePO. This topic comes up a lot when people are looking to replace there existing battery which is most likely AGM. The price of LiFePO batteries has come down considerably, manufactures have gone out of their way to limit your upfront cost by excepting a host of charging parameters. They still tell you of a high life cycle count that they have validated inside a laboratory (think how much power you get actually out of your solar panel compared to the laboratory method for sizing). So are we really going to get the numbers they are providing ?

The following is a list of things to do for long happy life of LiFePO batteries from a article on Solarcity.com How to Find Happiness With LiFePO4 (Lithium-Ion) Batteries
  1. Keep the battery temperature under 45 °C or 113°F (under 30°C or 86°F if possible) – This is by far the most important!!
  2. Keep charge and discharge currents under 0.5C (0.2C preferred)
  3. Keep battery temperature above 0 Centigrade when discharging if possible – This, and everything below, is nowhere near as important as the first two
  4. Do not cycle below 10% – 15% SOC unless you really need to
  5. Do not float the battery at 100% SOC if possible
  6. Do not charge to 100% SOC if you do not need it

Keep the battery temperature under 45 °C or 113°F (under 30°C or 86°F if possible). Everybody seems to know about cold weather issues with Lithium, but very few think of the high temps effects on lifespan. This is one of the big reasons that I highly recommend that Lithium batteries get installed inside of the van. The traditional under the van rack, even the fiberglass boxes through the floor don’t provide the insulation against the road heat, imagine the heat from the roadway in 100 + degree days. Depending on your battery or BMS they might even shut down at a higher temp setting.

Below is day in my van, the temp probe in the air conditioner (rooftop) is usually the hottest. The other temp probe is in the cabinet that houses my Truma Combi, it does have some venting. I was working on the van most of the summer, so the battery cabinet was open, and I didn’t have a probe installed. But you can see the benefit of having your battery inside in a cabinet.


Keep charge and discharge currents under 0.5C
Size your battery bank correctly, the general recommendation for discharge and charge rates is 0.5C. Most of the life cycle data is based on 0.5C charge and discharge rate. So if you are running an inverter on a consistent basis you are easily bumping needing over 150 amps of discharge capability. This puts you in the 300 amp-hr battery size. More importantly it is not hard to find a single 300 amp-hr LiFePO that only has a BMS that supports charge and discharge rates of 100 amps. So be careful on sizing your battery or batteries. Many times, you may need multiple batteries to get your discharge rate high enough.

Don’t discharge below 0°C or 32°F. This is the most well-known issue with LiFePO, and to be clear it does have an impact. But to be clear you can start out by moving the battery inside, also many LiFePO’s can be purchased with internal heaters. Some will be powered off of the battery itself, others can be externally powered, I have the heater for my battery attached to two battery sources, the LiFePo itself, or if need be I switch over to power provided by the Transit battery. For those of you worried about losing the power to heat your battery, remember you were losing significant amount of power to cold with your AGM battery,

Don’t discharge below 10% to 15% SOC. Although many LiFePO’s may advertise 100% discharge capability it is generally considered good not to go below 10%.

Do not float the battery at 100% SOC if possible. This is one of those that appears to be contradicted by the battery manufacturers themselves. They now appear to be happy to support a low float voltage. But again, that was a decision that was made to lower the cost of entry into the Lithium world. If you do have a charger that has a pure Lithium profile or 2 stage charger it might be a good time to use it, especially in the heat of the summer.
And while we are talking about charging profiles, let’s address the Absorption phase. With AGM batteries you generally have longer Absorption phases, some chargers even gave you the ability to increase the time in absorption depending on the depth of discharge. For LiFePO, the absorption phase should be relatively short. I believe BB says 30 min per 100 amp-hr battery.
The other phase that you should disable is automatic equalizing, LiFePO’s do not get equalized, if you can’t completely disable, at least set the equalize voltage the same as your absorption setting.

Finally, if you have any temperature compensation setting, they should not be used for LiFePo.

Do not charge to 100% SOC if you do not need it. This is one of the great features of Lithium compared to AGM. You don’t need to get if charged to 100% SOC. Remember partial SOC is one of the bigger killers of AGM battery life. When sizing your battery bank, you might want to look at 70% to 80% capacity of the battery for your target. This will give cover your #4 and #6. Generally during the summer my solar panels provide enough energy to replenish what I lose overnight. If I am leaving the rig parked in the driveway for periods of time, I may disconnect the solar for a day or two, this then allows solar to replenish power to the rig on a daily basis but not go over say 90% SOC so you don’t have to get into float. This doesn't mean you can't charge it to 100%, if your trip may need that extra battery time.

Speaking of SOC, a SOC meter is imperative to understanding the health and capacity level of your battery. The voltage drop-off for LiFePo is minimal, so if your use to using voltage for remaining capacity you will be in trouble. A SOC meter for AGM batteries is a good thing also. Currently the Victron 712 is a good SOC meter, that does well with Lithium. They also have the wireless Bluetooth unit, I recommend the 712, because it also has Bluetooth but also includes a programable relay that you might be able to use to say shut down your solar or DC to DC charger if you have reached a certain SOC.
I would only use one charging source at a time, so using a combined DC to DC/ solar charger is a good way to eliminate. In any advent you may want the ability to turn off your charging devices remotely. This is even more important if the combined units may force you over maximum charging current.

BMS Reset At some point your battery BMS might disconnect. While some conditions may reset themselves others may require some effort to get reset. The battery is basically disconnected from your charging devices, and many of these devices need to be connected to a battery to work. Most of the devices that have been developed for LiFePO have some procedure to work around this issue. Make sure you know what that procedure is what it takes to get your BMS reset if needed. So many LiFePO batteries come with an internal BMS. You might inquire what the possibility of changing out BMS if it goes bad on your battery. It should be cheaper than replacing a whole battery.

If you are installing with a large inverter, you may need a pre-charge circuit to make sure the capacitors are charged slowly before turning on.

While many of these best practices sound like a pain, they really are not that difficult to add to basic battery health procedures. Even if you don’t perform the last four, your battery cycle life will probably still far exceed your expectations and anything close to what AGM’s could deliver. And remember the specified cycles for an AGM were also best-case lab environment produced numbers.

-greg
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Old 10-01-2022, 10:34 AM   #2
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Nice write up! Once this topic comes up on my end I’ll surely read again :-)
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Old 10-01-2022, 10:36 AM   #3
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Excellent, thanks much for posting Greg.
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Old 10-01-2022, 10:52 AM   #4
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Super helpful! Thank you. As always, you are on top of this. You are an incredible resource for all of us.
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Old 10-01-2022, 11:32 AM   #5
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Great write-up Greg, well done.....

You covered having the battery sitting in the driveway jammed with 100% SOC all the time......we've all been conditioned to keep our batteries topped up since the self-discharge rate of lead-acid chemistries is relatively high, and leaving them partially charged for long periods of time can be detrimental to a long and happy battery life. LiFePo4 doesn't have these issues so storing partially charged is preferred.

I'm playing with lowering the float voltage when the van is parked for long periods to around 3.4V (or perhaps 3.3V) so that the time between charge cycles is very long.....easy enough to do with a Victron MPPT.....keeping the SOC well below full most of the time while the van isn't being used.

Another thing to possibly cover is the various settings in a typical battery monitor, Peukert's constant etc. I had some free time camping last week and went through my Linkpro Monitor; it seems to be tracking what my BMS is telling me very close....or more accurately the BMS is tracking what the battery monitor is telling me.

...and one more topic .....setting your upper and lower SOC, voltage, temp etc settings of your various chargers to a tighter band than the BMS.....ie the BMS stepping in and shutting down charging or discharging should be your outermost layer of protection.
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Old 10-01-2022, 01:39 PM   #6
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I had my Renogy BMS shut down the battery last month. Because of room limitations I had to mount my 4d LiFePO4 under the rig earlier this year and I'm thinking it got too hot sitting in my driveway and I was really hoping I wouldn't have to drop the battery - let alone replace it. Greg sent me the following suggestions:

I expect that you will at least need to provide a minimal charge to get a bad BMS to reset. If the voltage from the battery is below 6.5 volts the Kisae will not be operational. In that case, the following conditions may happen:

a) If the BMS disconnection to the CH1 output port occurs when the unit is charging from any of the two input ports, i.e. either the CH2 solar panel or CH3 starter battery and alternator (so with its display showing the normal charging messages of Volts, Amps, and charging stage), there is no problem as long as the charging voltage on the CH1 output port (provided by the unit itself) continues to be present until the BMS awakes (reconnects) the battery.

b) If the BMS disconnection to the CH1 output port occurs when the unit is not charging from any of the two input ports (i.e. the CH2 solar panel or CH3 starter battery and alternator) it cannot restart even when whatever of those input port sources becomes available later (i.e. by meeting their corresponding minimum Start-Up and Recovery voltage thresholds to start and continuing charging respectively).
In this case, one solution would be to temporarily bond the CH3 starter battery & alternator input port (never the CH2) to the CH1 house battery output port, until the BMS awakes the battery, as long as the minimum Start-Up and Recovery voltage thresholds to start and continue charging respectively, are met.
That bonding can be externally done using only the positive terminals and a piece of AWG #8 or #6 wire, provided that the batteries on both CH3 and CH1 ports are 12V nominal.
Note: Even though the unit does not get damaged with that CH3-CH1 external bonding, when the CH3 input port is available it produces a constant circuit loop at the maximum current as per the “h” setting (i.e. of 50A or lower) representing unnecessary stress for the unit (that maximum current is supplied and drawn at the same time by itself) except for the fact of awaking the CH1 house battery by its internal BMS. Therefore, it should be done temporarily and only for that purpose.

Essentially you are jumpstarting the BMS from the van battery.


I followed his recommendation for jump starting the battery and it fired right back up. That was a relief. I then followed his directions below for how to bypass the Kisea DC-DC charger while parked in order to keep the LiFePO 4 held at less than 100% SOC while not in use. Here's his illustration on how to do that on the Kisea DMT series chargers... pretty easy to wire in a basic on/off switch. I used an old phone cord I had laying around.

Thanks for your continued contributions Greg... another outstanding tutorial to bookmark for future reference.
Attached Thumbnails
BTS for remote shutdowns-011024_1.jpg   Switch.jpg  
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Old 10-06-2022, 11:27 AM   #7
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We have a circuit breaker/switch in between our solar panel and our charge controller, we also have a switch for our DC/DC charger. This allows us to disengage all charging sources and/or enable the one we prefer at the given time. After speaking with BattleBorn they told me the most important was to fully recover when we charge and not do a partial recharge if we don't have to. So instead of stopping at around 88%, what a friend does with a different make of batteries, we let ours run down over three days to about 45-55% then fully recharge to 100%. Now that we are not full time we try to have the bank around 60% as that is the recommended SOC for storage, again according to BattleBorn. If we are planning a trip we either use solar or a battery charger (with a Lithium profile) to get the bank to 100% the day before and don't utilize any charge sources for just a weekend jaunt. Time will tell if the switch from AGM was worth it but for a weekend rig (non-fulltime), based on how we consume power, we recommend AGM as it is a much more set it and mostly forget it system.
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Old 10-06-2022, 12:56 PM   #8
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So I agree and disagree somewhat with the battleborn information. LiFePo and that includes Battleborn do not suffer cycle life damage from from partial state of charge. Having said that I would agree that you need to perform a full charge cycle periodically. And by that I mean getting the battery up into the absorption stage of charging. As this is the stage where the BMS performs any cell balancing activities. So just charging to 80% or 88% would not be a good long term thing to do. I do apologize for any disinformation I may have provided by not making that clear.

-greg
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Old 10-06-2022, 01:10 PM   #9
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Quote:
Originally Posted by Scalf77 View Post
So I agree and disagree somewhat with the battleborn information. LiFePo and that includes Battleborn do not suffer cycle life damage from from partial state of charge. Having said that I would agree that you need to perform a full charge cycle periodically. And by that I mean getting the battery up into the absorption stage of charging. As this is the stage where the BMS performs any cell balancing activities. So just charging to 80% or 88% would not be a good long term thing to do. I do apologize for any disinformation I may have provided by not making that clear.

-greg
It was clear, I just wanted to add what we were told directly by BattleBorn. I actually called them twice and spoke to two different individuals to make sure I was 100%. They even reiterated it in email. While they market their batteries as 'drop in' replacements I was hesitant to let them fully recharge every single day based on the experiences of a very good friend (a retired Royal engineer). He has his system set to recharge to ~88% daily and only up to 100% once per month, based on the technical specs of his batteries, which is the optimal charge pattern for extended life. I can't remember the brand as they are a European make.
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Old 10-08-2022, 11:29 AM   #10
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Very nice explanation for charging LiFePO4 batteries. Like you, I have a Transit (2019) that needs charging of the starting batteries (dual AGM’s) periodically to prevent a possible dead battery situation. I have noticed that my house LiFePO4 batteries receive a trickle charge when the start batteries are on the charger. Like @bigriver, I too have shut off switches for the DC/DC charger and the MPPT solar charger. I’ve used these switches in very cold weather while winter camping but have not used the DC to DC shutoff in the summer. We live in Phoenix and the inside of the van may get to 117 F during the day. Our house batteries are located within the van which I monitor with Victron 712, also. The van battery temps have been as high as 42C (107F) this summer. From looking at the graph you presented, I’m definitely going to shut off any trickle charge to my house system using the shutoff switches when it’s hot here. BTW the on/off house switch does not prevent the “trickle effect” when the start battery is charging. Thanks for imparting this useful information.
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