Welded vs. bolted busbars

[tigerwillow1]

One of the advantages I imagined with LiFePO4 batteries was that if one cell died it could be replaced instead of pitching the whole battery out. I see that pretty much all of the preassembled batteries use welded busbars, which I figure pretty much eliminated the possibility of replacing a cell. I can see the welding as a big advantage in a mobile application, not so much in a stationary application like residential backup power. Welding the busbars obviously reduces the chance of a failure, but is giving up the capability to replace a cell worth that small reliability improvement? I see it as comparing the risk of a loose busbar connection in a stationary battery against the risk of a cell going bad. Is there an obvious answer to this?

Driving the question is four of my 12 volt AGM batteries, each with one bad cell.

 

[chrisski]

I did not know the smaller lithium batteries were welded inside. The few take part videos I saw were 4 cell type batteries and I thought they were all screwed in.

I do think huge, high ampreage battery packs with many, many parallels cells or batteries have welded busbars to the battery terminals because resistance being off in one of these huge, expensive, paralleled packs can cause one set to drain way quicker than another set meaning the whole pack needed replaced.

 

[fafrd]

One of the advantages I imagined with LiFePO4 batteries was that if one cell died it could be replaced instead of pitching the whole battery out. I see that pretty much all of the preassembled batteries use welded busbars, which I figure pretty much eliminated the possibility of replacing a cell. I can see the welding as a big advantage in a mobile application, not so much in a stationary application like residential backup power. Welding the busbars obviously reduces the chance of a failure, but is giving up the capability to replace a cell worth that small reliability improvement? I see it as comparing the risk of a loose busbar connection in a stationary battery against the risk of a cell going bad. Is there an obvious answer to this?

Driving the question is four of my 12 volt AGM batteries, each with one bad cell.

If replacing cells is a priority, welded flat terminals that are specific to individual cells and can be connected to their neighboring cells with a bolt or two offer the best if both worlds…

These soft aluminum terminals were never designed to be threaded and that is a cause of many failures and possibly also a safety concern…

 

[Mcgivor]

Driving the question is four of my 12 volt AGM batteries, each with one bad cell.

The association with cell failure in lead acid is not something to be over concerned with when using LiFePo4, as the cells do not fluctuate in voltage, as is the case with lead acid , where a single cells failure can be masked by the ballance of cells working harder.

When using a BMS, any excursions from normal cell level parameters, should result in battery disconnect so the possibility of individual cell failure is greatly reduced.

Welded vs bolted? Both have strengths and weaknesses, depending on the quality of the initial installation, the emphasis being on the word quality, manufacturers use welding as it is more consistent, labor/cost saving as well as offering tamper resistance.