Can I mix 1yr old EVE 280ah with new EVE 304ah?

Can I mix old and new and different size? I have an 8 cell 24v pack and need to go to a 16 cell 48v pack. Is this OK?
The delta on the 280's is still very good. I run between 25%-90%.

The capacity of the whole pack will be limited by the lowest capacity cell. I.e. if you have one 274Ah cell, the whole pack is now only a 274Ah pack.

Aside from that, it can work.

The resulting battery will behave a little strangely at the bottom end: you’ll have eight cells in the lower knee of the charge curve and eight still in the flat part. So you might have the BMS cutting off when the battery voltage is higher than normal, maybe around 47 volts (just as an example, 8 cells at 3.2V, and 8 averaging 2.7V, with one down to 2.5V).
This isn't really that big of a deal, just keep it in mind. It might be relevant when you’re deciding on a low voltage cutoff for loads.

OffGridIdaho said:

Can I mix old and new and different size? I have an 8 cell 24v pack and need to go to a 16 cell 48v pack. Is this OK?
The delta on the 280's is still very good. I run between 25%-90%.

Click to expand...

My two 8s 24 volt battery packs have both 271ah and 280ah CATL cells. They run real good in the flat part of the curve, but in the lower & upper knee the voltage of the 280ah cells does vary from the 271ah. The packs run approximately (5% 24 volts) to (99% 28.5 volts). The lower 24 volts is not a problem although there is some voltage difference between the 271ah & 280ah cells. The upper 28.5 volts in absorb can be a problem with some cells running and tripping overvoltage limit using an Overkill Solar BMS that has minimal balancing ability. The problem was corrected with a Heltec active balancer (turn on at 27.5 volts) on both packs and holding at 28.5 volts for 20 minutes each time in absorb to balance the cells. JK BMS with 2amp balancing would probably do the same.

Suggest stick with the 280ah Eve cells for the battery pack expansion. They will probably work better. I only went with the 280 cells because could not find a good source for the 271 cells to replace some that were excessive runners.

I have issues (although manageable) with only 9ah difference between the cells. 304-280 = 24ah suspect it will be more difficult.

Why spend the additionsl 15% for the 304ah vs 280ah to put in series with other 280's? It doesn't get you anything.

Now, if you had old 304's, and needed to expand, then you may consider adding 280's because of the diminished capacity of the 304's.

TBH you are asking for Quirks & Foibles, not to mention tempting Murphy's Laws heavily !
Seriously, get another 8 280AH cells and build a proper 48V/280AH Pack. The prices continue to drop and both V2 & V3 EVE cells are readily available. Then the next pack you build could be 304's or whatever and you won't have issues.

OffGridIdaho said:

Can I mix old and new and different size? I have an 8 cell 24v pack and need to go to a 16 cell 48v pack. Is this OK?
The delta on the 280's is still very good. I run between 25%-90%.

Click to expand...

Not a good idea in series, cells or batteries. You can parallel packs of different capacity, I have a bank of 4 batteries, one battery is 304 Ah and the rest are 280 Ah.