Do I really need to put cells under compression or just be able to withstand expansion?

[Pappion]

If I were to do compression, I would use springs or belleville washers. To set a known compression and allow for temperature expansion and contraction.
I did not bother in the rush to get it done. Also did not want to use flammable wood. I am not running high currents for Inverter, so it's not likely I would benefit from compression.
BTW: My solid bussbar between terminals have a bend (hump) and slotted holes. They seem better for temperature changes.

 

[JJJJ]

For those who install their systems in a moving vehicle, then movement would be a consideration. A good flexible bus bar might be a consideration.

A friend has field stripped Tesla batteries. These have the potential to be exposed to some fairly extreme conditions. They have coolant systems built in to control temperature. They are also interconnected by fine wire. The packs I have seen were glued together, so while not compression, this could mimic a fixture to prevent movement.

Granted this is a different chemistry. The take homes for me are controlling temperatures where my batteries are stored, keeping them safe in a location so they are not bumped and moved around, utilizing lower C rates for charge and discharge and setting the operational voltage levels to conservative settings.

I don't worry about the calendar age. If I were installing these in a commercial application where they were required to run for XX years without maintenance then that would be a different conversation. In that case I would be installing a commercially prebuilt battery for that application.

 

[TomC4306]

When using this in an RV/truck/whatever, this would worry me. Especially when using solid busbars between terminals.

I'm NOT using them in an RV/truck/whatever(?)
They're sitting in my basement powering my house

 

[DIYrich]

This is conjecture, and not supported by any studies I have seen. I'll ask again, how long is the calendar life of modern EVE cells?

Based upon below, I would guess that batteries kept under 85°F degrade about 3% per year, maybe 2% if kept under 75°F.

https://www.frontiersin.org/articles/10.3389/fenrg.2023.1108269/full#:~:text=For LFP, degradation is less,low as compared to NCA.

Temperature, SOC and time are key factors related to calendar aging in LIBs via three main mechanisms: loss of lithium inventory, loss of active material in the electrodes, and a rise in cell internal impedance.

The primary cause of loss of lithium inventory is the consumption of Li-ions by side reactions, including the creation of solid electrolyte interface (SEI) on the surface of graphite negative electrodes, the electrolyte breakdown processes and binder decomposition.

Loss of active material is often caused by electrolyte decomposition, and electrode particle cracking during storage.

Internal impedance in LIB increases owing to SEI growth, electrolyte degradation, and binder decomposition during storage.

Most researchers have concluded that the aging process slows down at low SOCs.

For LFP, degradation is less than 1% per year at 20°C (68°F) and 10% SOC. Even for temperatures ranging from 20°C to 45°C (68°F to 113°F), LFP show less than 10% capacity degradation per year.

https://uwspace.uwaterloo.ca/bitstream/handle/10012/12177/Catton_John.pdf

Cells stored 35°C, though, do not reveal a major decrease in capacity. Despite the long duration of storage, the capacity charge and discharge voltage curves only showed a small decrease in capacity.

whereas cells stored at 35°C (95°F) only experienced just over 10% loss in capacity despite being stored for over two years.

 

[Martijn]

I'm NOT using them in an RV/truck/whatever(?)
They're sitting in my basement powering my house

Good