Connections

Making a battery pack requires joining cells together, it goes without saying that this has to be done with some sort of conductive material so that current can flow and power the load. In large battery banks this is done with cables that get bolted to studs on the battery.

But using cables doesn't make sense for small battery packs, so what do we use?

The most common material used to join cells in a battery pack is nickel. It exhibits a low resistance and high conductivity. Copper exhibits even better characteristics in this regard but is difficult to spot weld to cells.

Spot welding is achieved by passing a very high but short pulse of current through two clamped pieces of metal. The current flows from one electrode through the first piece of metal, then to the second piece and finally to the second electrode. The electrodes we use are copper and of lower resistance than the nickel and cell connection, therefore the nickel cell connection heats up and causes the metal to instantly melt and combine.

During the process of designing a battery pack the required thickness, width and length of the nickel strips to be used are calculated. Thicker nickel strips, wider if the assembly allows it, may be chosen for high current areas of a pack, and thinner more narrow for low current areas.

Sometimes nickel coated steel can be used as tags and inter-cell connections if the application allows it, as in low current packs. Sometimes it is simply done for cost cutting purposes.

Nickel coated steel may corrode, in time this could be a problem. Nickel coated steel also comes with a 50% increase in resistance so for any given pack design your losses will increase due to this. Quite often the efficiency of a pack, particularly if it is required to supply a high current, will be determined as much by the inter-cell connections as by the choice of cells.

We don't use nickel coated steel at all but will always use 99.9% (confirm) nickel for our inter-cell connections. It just is not worth the loss in your confidence with our product to use anything else.

Sure, pure nickel tags and connections are a bit more expensive, but in the long run you want a pack that is as efficient as possible, will not prematurely fail due to corrosion or have overheating connections due to high resistance.