batteries continuously charged at 98 to 100 percent.

[Rusty1946]

I have two eco-worthy 14.3 k batteries that when I am running on grid, the grid keeps the batteries at 98 to 100 percent charge. when i go to off grid mode, the batteries will go down to 50 percent until the solar panels kick in and charge up the batteries to 100 percent. The advantage of having my system on grid mode is that we send electricity back to the grid and we produce more electricity then we use, allowing us to receive money back from our supplier, at trueup.
Will keeping the batteries at 98 to 100 percent for months or a year hurt them? We seldom loose power from our supplier. We purchased these batteries and a extra off grid inverter for (just in case).
Thanks

 

[SunDave]

If you have batteries, and you are worried about keeping them at 98-100% why not use them at night down to a certain %? Unless there is a storm in the forecast you are using grid power at night when you don't need to be.

Maybe I'm missing something. I have batteries, and an inverter and I run on battery all the time. You can just set a % to use down to while on grid. 70% or whatever you want.

 

[robby]

Yes keeping LFP batteries at 100% is going to shorten their life,
Discharge at night as suggested.

 

[SunDave]

One other benefit of using the battery is that you will know if it works when you need it. Like everything else, a system not used is a system that won't work when you need it.

For example, if your battery is unbalanced, or something else is wrong with it, you won't know it until the power goes out. However, if you use it on the regular you will know what to expect. Just a thought.

 

[Tulex]

I've always heard that you don't get anywhere near as much for selling as you pay when buying. So why not use the batteries to not have to buy?

 

[robby]

I've always heard that you don't get anywhere near as much for selling as you pay when buying. So why not use the batteries to not have to buy?

There are some utilities that pay 1:1 in the daytime and give you free power after a certain time in the evening. I think one person said between 10pm and 7am he pays nothing.
He uses the solar and batteries in the day to sell as much power as allowed and charges his batteries at night from the grid.
When he told me he was getting free power at night and making a sizable sum from what he sells in the day, I was shocked.

 

[1ufvlsi6x]

EVE says in specs to keep LFP batteries between 10 and 90%. There is a way to sort of reliably do that daily without even fiddling with coulomb counters that much (which drift anyway); just charge with 54.4V (3.4 per cell otherwise) without extremely high C; it should settle at around >=90% anyway.

This isn't a completely random number; the base physics of LiFePO4 let it generally be at a steady ~3.4V when charging and 3.3 when discharging (when the C isn't extreme); all signs indicate it's the best way to have your pie and eat it too (both charge quite high and keep it reasonably healthy).

 

[Tulex]

There are some utilities that pay 1:1 in the daytime and give you free power after a certain time in the evening. I think one person said between 10pm and 7am he pays nothing.
He uses the solar and batteries in the day to sell as much power as allowed and charges his batteries at night from the grid.
When he told me he was getting free power at night and making a sizable sum from what he sells in the day, I was shocked.

I forget there are weird plans out there. We pay the same all the time. We have net metering here, I have no idea what it involves, I'm not selling back.

 

[robby]

Mine was offering one third payback.
I told them no thanks.

 

[Brett V]

I have 1:1 net metering. Hopefully it lasts a while but realistically I know this is economically unsustainable for the POCO.

OP: when you say 98% - 100%, what is the voltage? Anything at or below 3.5v per cell won't hurt them.

 

[robby]

Sustained full charge will start to create dendrites at the cell separators.
Keeping the charge will make them grow even faster.
That is why batteries are stored at 40% SOC.
They are your batteries, so obviously you can do what you please with them.

 

[timselectric]

Leaving them full isn't a problem. But Keeping a long extended charge on them is.
Once full and balanced, either turn off charging, or reduce the voltage to 3.375 per cell (54v).