There are a few ‘Rules of Lithium’ for which we’d love to see justification.
The first: Lithium batteries should not be maintained at 100% charge for long-term storage.
This may well be, but we’ve never discovered any studies to document this. And without a ‘study’, we are left with the question: If 100% is not good, what percentage is good? 90%? 80? Less?
Turns out, for us, between time actually ‘on-the-road’ and periods where we’re ‘piddling’ with the van - - we keep the ProMaster ‘on’ most of the time. Normal use is long-term in our case. It would appear that whatever the ‘magical’ long-term storage SoC is - - we should adopt it for our normal in-use target.
Then there’s the oft-repeated “Rule” that Markopolo quoted: “LFP batteries do not need to be floated.” Or, worse, they “should not be” floated. Again, we have found no data to support this Rule and question, as noted below, its logic.
This Rule has caused several of our compatriots to shut-off their charging sources even during periods of actual 12 volt use. They do this - - thereby cycling their batteries - - even at SoC levels well below 100%, in the belief that to do otherwise would be to improperly Float their lithium packs.
Discharging and recharging our batteries is normal while dry camping - - it is, in fact, why we have batteries. But why cycle our battery packs when alternate sources of energy are available? Unless, of course, Floating is evil.
Our position is that leaving ones ‘charger’ on is not really Floating the batteries. First, let’s not call it a charger. Why not call it a power supply? What’s wrong with having a 12 volt power supply to provide the necessary 12 volt energy?
And how do we justify that leaving the power supply on is not Floating?
At Post 78 of this thread we offered a table of Resting Lithium Voltage vs SoC. As we don’t know what a good long-term SoC should be, we’ll just arbitrarily pick one - - say 90%? Our data establishes that 90% SoC equates to 13.36 volts. Unfortunately, none of our charging sources (power supplies) allows us to program them with 1/100 volt precision (and, even if we could, the manufacturers have told us that their equipment can only hit a programmed number +/- 0.1 volts anyway). So we have to choose either 13.3 or 13.4 - - we’ve erred on the high side: 13.4 volts.
In support of our assertion that maintaining our 13.4 volt power supply isn’t “Floating” the battery, we note the following. If we start with the battery ‘resting’ at 13.4 volts (90% SoC), attaching a power supply of exactly the same voltage . . . causes no change. The battery pack continues to ‘rest’ - - it is neither being charged, nor discharged. Some will call this “Floating” . . . but if it is Floating, the battery doesn’t know it’s floating and the connection of that power supply cannot in any manner cause damage to the battery.
The advantage to this arrangement occurs when loads are applied - - the normal situation when camping. The 12 volt current required by any load is, effectively, being supplied by the power supply, not the battery - - thereby avoiding what we contend to be the needless discharge/recharge cycles (that our noted comrades are imposing on their lithium systems in fear of Floating them).
The point of this somewhat lengthy addition to the present thread is this: You can probably set all your charging sources to 13.4 volts and be assured that, at some point in time, your lithium reservoir will be at 90% SoC. This is what we (mostly) do. The only time we take our chargers to 14 volts and higher is when we want to quickly restore depleted batteries or, on rare occasions, to implement our systems ‘shunt resistor’ cell balancing system.
I had assumed it was the voltage at which one wanted charging to be maintained at. I now think 27 FLu is the better choice.
