Have a look at these threads, read the first one to the end. 

 

https://thegreynomads.activeboard.com/t67732755/lithium-batteries-charging-discharging-balancing/

(Link to the very thorough article in first post)

 

 

Some teardown examples:

 

https://thegreynomads.activeboard.com/t67455852/lithium-battery-teardown-examples/

 

 

Get a quality brand with an inbuilt 'battery management system' (BMS) and yes they can just drop in as a replacement.
Just make sure your current lead-acid charge setting does not have the rejuvenation feature turned on.
Lithium can be discharged as a battery but Lithium requires charging to individual cells rather than as a battery because once a cells voltage reaches the charging voltage it then does not pass ions along the series to the next cell in the chain.
The BMS will take care of the charging and control the maximum charge and discharge currents.
With 4 cells at 3.65V per cell you need 14.6V to fully 100% charge a "12V" LiFePO4 battery. Your standard Gell/AGM setting will charge it to 14.4 volts.
Unlike lead-acid cells that have a chemical conversion take place with the lead sulphate (PbSO4) and water (H2O) changing back to lead and sulphuric acid ( Pb + H2SO4), the nature of lithium is that when combined with various other minerals it can hold excess ions (electrical charge), hence the generic term Lithium Ion.
Unlike lead-acid, whatever voltage you apply is what the lithium charges up to, there is no excess charging by applying that voltage for an extended time. If you apply 14.4 volts then the cells will be balanced up to 3.60 volts by the BMS.
There is no need to continue charging at 14.4, if that is what you supply then that is as far as the battery will charge to, so in the ideal world you charge Bulk to 14.6 and then stop charging whereupon the battery will settle to around 13.4V and when the battery drops to 13.2 the charger starts back up again. There is no need for absorption or float charging, but if that is what your current charger does, the only downside is that the charge process is not as fast as just bulk charging.
Surprisingly, Lithium does not care one bit if you don't fully recharge it and will quite happily exist at whatever charge state amount you so choose 50%? 75%? 90%?.
Charging wont start until there is 3.2V per cell (12.8V) which will take them to about 25-30% state of charge and at 3.55V per cell (14.2V) your cells reach 98-99% charge, so a specialised 14.6V charge is not really required just for that extra 1-2%.
Once cells receive voltages 'over' 3.7V per cell (14.8V) they start to warm up a bit and that should be avoided.
It should be noted that a flooded wet cell lead-acid battery ideally uses a 14.7 V bulk charge so that wont damage your lithium either.
Another positive of lithium is its very low internal resistance so you can expect somewhere around a 30% increase in solar and 240V charger charge currents resulting in faster charge times compared to lead-acid batteries even from old style chargers.

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-- Edited by Hylife on Sunday 22nd of January 2023 08:49:52 PM

StormCamper wrote:

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The story of lithium not getting fully charged is fishy indeed, lifepo4 can be fully charged with as little as 14v, 

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 Redarc BCDC dc to dc  chargers have a float voltage of 13.3v. It has been found that with these chargers used on Lithium 'drop in' batteries that the batteries will go into float mode prematurely before they are fully charged. In fact they will only charge to a maximum of about 70%.  Redarc have confirmed this.  I may have been incorrect about the issue being BMS related - not sure on that, but definitely not all non Lithium profile chargers will fully charge Lithiums. The BCDC chargers with the lithium profile manage just fine. This may well be a case of 'ridiculous smarts'. I have never really liked that my BCDC1240 floats at 13.3v, lower than the recommended float voltage for most AGM's, done I believe as a cheap way to avoid the need for temperature compensation. That said though, the first set of AGM batteries I had on the BCDC1240 lasted almost 10 years, so the low float voltage doesn't appear to have been harmful, but will need changing if I ever switch to lithiums. 

-- Edited by Cuppa on Friday 3rd of February 2023 10:29:14 AM

StormCamper wrote:

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The story of lithium not getting fully charged is fishy indeed, lifepo4 can be fully charged with as little as 14v, hence the gel setting being often used. As the battery gets bigger and drive times longer than even low voltages of 13.5 will allow alot of current to flow and so a low voltage may be moot. A well regarded brand is very different to a well designed good charger, some chargers have ridiculous smarts. People praise victron yet they have their many issues. Bottom line, buyer beware, you don't buy expensive batteries without doing your research. One nasty side of lithium is that many chargers can't run at high output in high heats without having to throttle back so the charge times become AGM like. Lithium require high output for at least a few hours....

I'm sorry Hylife is wrong about 14.7V not damaging your lithium, again do your research or get in trouble. Yes nothing bad will happen, but that voltage is too high and combined with long absorb durations is a dandy good way to shorten the life in the long-term, amazing the advice you get on forums haha.

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 No, it is I who am sorry StormCamper, for it is you who is very probably wrong.

Lithium cells are NOT charged as a battery, they are charged as individual cells by the BMS.

After decades designing IC circuitry, I have yet to see a large capacity BMS (it is possible that they may exist in someone's home brew set up), that operates as a single output DC to DC voltage converter that then feeds into 4 or 8 individual controllers.
Such a controller if they were ever to be manufactured for large capacity batteries could theoretically 100% charge your 4 lithium cell battery with as little as a 4 volt input (allowing for a little loss in the circuits). I say large capacity because the only such BMSs that operate in this manner are low capacity chargers power tools.

StormCamper, please understand that the BMS for a high capacity lithium battery such as those used by RVs are simple voltage splitters. The circuitry simply takes the input voltage and divides by 4 or 8 for 12 or 24 volt systems and supplies that voltage to each cell. Once each individual cell reaches 3.65 volts the individual split shuts off its output but the other splits will continue. In this way the cells are balanced each time they are charged and the charge current can be shared across however many splits are still charging. (remember the old Ohms law bit about amps and volts)

LiFePO4 cells do not commence storing excess ions until the cell terminal voltage exceeds 3.2V per cell. At that voltage a LiFePO4 cell will charge to between 25-30% capacity. 3.2V per cell requires a 12.8V input.

LiFePO4 cells heat up from current flows, NOT from voltage unless the terminal voltage exceeds 3.75 volts per cell or 15 volts from a 4 cell split.
14.7volts in a 4 cell split is 3.675 volts per cell and will NOT cause any damage to cells.

Stormcamper, I have many years of R&D with charge circuits for many different Lithium chemistries. Your statement of charging with 14 volts is going to present each cell with 3.5 volts only if the circuitry has zero losses. This will unfortunately only get your cells to around 80%.

Scubadoo wrote:

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. Both my shunt based battery monitors agree to within 1 or 2% SOC.

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 May I ask what shunt type monitor you have?  Is is one of these types:

https://www.outbackequipment.com.au/hrdkorr-remote-battery-monitor-with-high-precision

or;

https://itechworld.com.au/products/itechbm500-500-amp-battery-monitor-with-shunt-high-and-low-voltage-programmable-compatible-with-12v-lithium-sealed-gel-flooded-batteries?_pos=1&_sid=a12d30145&_ss=r

 

Both above look identical, likely from same factory.  I have the HardKorr one as posted above.

Now I ask my question if you have one of the above as I cannot find a answer to a setup on the monitor.  Setting the initial voltage on the monitor is either to zero as Itech world world say in a video, or at 10.5v as a flat battery voltage on LiFeP04 as some other videos show,  or actual battery voltage from a volt meter at time of setting this up. 

Anyone know the actual answer to this? 

Cube wrote:

May I ask what shunt type monitor you have?  ...

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I have used a few shunt based monitors over the years and now have a 500A Victron Smartshunt with a dedicated old phone permanently monitoring the Smartshunt, solar controller, inverter, battery charger, Battery Protect etc. data.

The other battery monitor is an $80 400A Junctek KG140F purchased via Aliexpress.

Both perform perfectly but for casual viewing and monitoring the much cheaper $80 Junctek is my favourite. It can also display the same data wirelessly on a phone or tablet.

A far from perfect photo of my setup with both monitors matching at 65% SOC.

 

It's true that you can often replace AGM batteries with lithium battery without needing to change other equipment like solar controllers or chargers. However, it's crucial to ensure compatibility and adjust settings if necessary. Lithium batteries have different charging characteristics, so you may need to reprogram your solar controller or charger to optimize performance and prevent overcharging.

-- Edited by Gregoryrg on Wednesday 27th of March 2024 10:22:44 AM