locked Re: Batteries starting to get weak - MMM - What to do -

Scott SV Tengah


My Victron BMS reports cell level voltage down to 0.01v. I can view it via bluetooth and have seen it vary by 0.01v.  I can attest that when I had an imbalance, up to 90% SOC, the cells had the exact same voltage, down to 0.01v. Above that, the variance reared its ugly head. This is not theory - this is my experience living with this system fulltime for 2 years. So I would be very skeptical of any active balancer that has the same resolution as you may be unknowingly exacerbating an imbalance by relying on marketing promises.

If I haven't stated before, I do agree that if you want a system that requires no planning and very little monitoring aside from making sure you don't go below 50% SOC, then lead batteries are fine. If I were in your position and spent most of my time plugged into marinas, I would probably NOT get lithium even if someone paid me to take it. 

One guy may have had his gel batteries last 9 years, but longevity is not the main reason we got lithium. As we speak, I am running the dishwasher and washing machine and the admiral just turned on the microwave - all on battery/inverter. The continuous draw is around 160amps and the voltage is quite stable. Because of the huge boost in charge efficiency compared to lead, I won't be running the genset to recharge the batteries, either. Our solar is more than enough.

But as economists like to say - there is no free lunch. Lithium requires planning and thinking prior to implementation and if you plan it right, it is set it and forget it. I am not quite there but moving in that direction slowly. The same thing applies if you compare roller electric in-mast furling vs. manual stacking mainsails. The former requires some thinking but, at least to me, is well worth the effort. For my use case, lithium is the same. 

I hope my contribution to this forum is useful in that those who are off-grid and would rather not run the genset all the time are given some useful info that they can use to plan their systems. It is beyond my risk tolerance to try to assemble battery cells and rely on them in the middle of the ocean, so I went with a mostly-one-brand solution that allows me to monitor every single of the 24 cells via bluetooth and if a cell fails, quickly remove that battery pair and continue on with my trip. Luckily I haven't had to do that yet.

On Wed, Sep 23, 2020 at 9:34 AM Arno Luijten <arno.luijten@...> wrote:
Hi Scott,

Typically good BMS-es can measure at 0.01 resolution. So even at lower SOC you will be able to see differences. Charging up to 100% can be postponed longer with continuous balancing. Active balancing means you are using the charge of the fuller cell to charge the less full cell. That improves the speed of balancing and prevents useless heat generation.
Obviously it's not as world of difference all together but if you design a BMS for lithium you may as well make it top notch. The system is expensive enough to push it to the limits of longevity.
Your battery-monitor has a easier life with lithium as the charge/discharge losses are far less so it will keep an accurate reading longer, especially if you can set the Peukert value yourself.

If you are less concerned about those things than I think the Battle Born 24V batteries are a good choice, just do not expect 10-15 years of life. If you do achieve 10-15 years you can always celebrate at that time, but at least you will not be disappointed.
As said before and as said by others as well; there is still so much development in this area that I prefer to wait a few years to see what the next best will be. I just read something about a person managing 9 years on some Gel batteries so it's not that all other chemistries are useless.


Arno Luijten
SV Luna,

2007 A54 #69
SV Tengah

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