Domestic battery bank: lowest life cycle cost?

[GHA]

One of my worries about lithium is that if you do damage the bank somehow- e.g. faulty charger, or accidental short etc- then you are writing off several thousand pounds worth of batteries. With cheaper batteries, the risk is much lower.

Agree with that , certainly for cruising. Zap the bank and you could be stuffed with a charging system which won't be any use for whatever batteries you can actually lay your hands on locally in some far flung corner of the globe. Pity really, they do have a load of advantages, price not being one..

Might be worth having a location which has enough height for t105's or similar even if you decide on something else, over the decades an awful lot of cruisers have asked the same questions, trojans have ended up being highly regarded on a cruising boat through trial and error over the decades. The long distance cruising crowd are a hard bunch to please

 

[Graham376]

Zap the bank and you could be stuffed with a charging system which won't be any use for whatever batteries you can actually lay your hands on locally in some far flung corner of the globe.

What's the difference in the charging regime? This link indicates 14.6v - 14.8v with float 13.8, which is reasonably similar top Trojan or AGM. https://www.qualitysource.co.uk/sto...qIbuh5mcOykAYPn8zzVwibZL2BtkEbHEaAv_TEALw_wcB

 

[GHA]

What's the difference in the charging regime? This link indicates 14.6v - 14.8v with float 13.8, which is reasonably similar top Trojan or AGM. https://www.qualitysource.co.uk/sto...qIbuh5mcOykAYPn8zzVwibZL2BtkEbHEaAv_TEALw_wcB

Not sure exactly other than it's complicated

https://marinehowto.com/lifepo4-batteries-on-boats/

DURATION AT TARGET VOLTAGE:

One area folks often misconstrue is thinking a lower charge voltage means it’s 100% safe for the LFP battery. It may not be. If your charge sources are not suitable they can still over charge by holding the constant-voltage stage (absorption) for too long. Over absorbing, even at pack voltages as low as 13.68V, can result in charging to 100% SOC. Continuing to charge beyond the point where the Li-Ions have stopped moving from the cathode to the anode would be considered “over charging“. Over charging can lead to a phenomenon known as lithium plating. If the CV (constant voltage) stage of the charger is held long enough an LFP cell can be fully charged at voltages as low as 3.42VPC.


Most lead acid designed charge sources can hold the absorption voltage stage more than long enough to cause long term damage to your expensive LFP cells. Some LFP manufacturers are now starting to understand this point, when selling into a lead-acid charger environment, and have reduced recommended max charging voltages accordingly, though some others have not.


I recently had four prismatic cells in the shop, sent to me by a gentleman who assumed a GEL setting on his charger was safe. He decided this based on Winston’s voltage specifications. He assumed, seeing as it was only 14.1V or 3.53VPC, and well within the spec, that 14.1V was safe for a nominal 12V bank. However, as I mentioned earlier, voltage is not the only factor to consider. You have voltage, duration at target voltage, and charge rate to also consider. LiFePO4 cells are optimally charged to 100% SOC then charging is terminated/stopped. This was the original design of the chemistry. This does not happen with far too many lead-acid designed chargers so you as an owner will need to chose charge sources that can be carefully programmed..


The problem the GEL setting installation was the absorption DURATION, not the voltage. At 14.1V the absorption duration was 4 hours long with no way to change the length of the absorption cycle-timer. On top of a 4 hour absorption the chargers charge rate, which was very low in comparison to the banks Ah capacity, his cells were actually hitting 100% SOC before the voltage even got to 14.1V. Continuing to charge beyond the 100% SOC point can lead to lithium plating.


In other words he was technically over-charging his bank before he even got to 14.1V because charge rate also plays a role. Once his bank hit 14.1V the charger then continued to charge them for four more hours each time he went to 100% SOC. On top of all this his so called “smart charger” was actually really quite dumb and could reset the absorption timer when ever a large load kicked in and momentarily dropped the sensed voltage below the re-absorb trigger.


In just 150 +/- cycles his 180Ah cells could barely deliver 96Ah’s and they were puffed up like balloons. 2000 cycles? His expensive Winston LFP cells were severely diminished in less than 150 cycles while using the GEL setting we so often read about as being “safe” for LFP. If his charger had stopped charging when the cells actually hit 100% SOC, it would have been much safer, but instead it kept charging for 4+ hours after the bank was full and could easily be re-triggered back into an absorption cycle pretty easily. Considering the boat spent much time at a dock it is impossible to say how many horus they were maintained at 14.1V/3.53VPC..

 

[Graham376]

Yes, seems complicated but this statement in the spec. would appear to cover the overcharge situation - Each LiFePO4 battery has an internal battery management system (BMS) that protects the battery against over charge, over discharge, short circuit, and high temperature. Don't think I'll be buying anyway as they most likely have more cycles than I have left

 

[overstag]

My Mastervolt Lithium battery is charged from three possible sources. All with a dedicated lithium regime and inter-communicating through a common data bus. As stated above, it is different from any other charging method. It doesn’t go to float ever. It just swithes off when it reaches 100%. And doesn’t switch on again until it has discharged a fair bit.
Still optimistic about this being the last battery I’ll ever buy.. ;-)