A solid metal bar that acts as one shared connection point, so several cables can join the positive (or negative) side neatly instead of stacking on the battery terminal.
Stacking five ring terminals on one battery post is how loose, hot, dangerous joints happen. A busbar gives every cable one solid, shared landing point instead — cleaner, safer and far easier to inspect.
There is a positive busbar and a negative busbar. Charge sources and loads all land on them rather than directly on the battery, with the main fuse and switch between the bank and the positive bar.
Design your van, boat, cabin or RV system in Wattonomy and it places the positive and negative busbars in your wiring diagram and routes every conductor to them, so nothing stacks on a battery terminal — from the appliances you actually run, sized to the recognized standard for your region. You see it on the wiring diagram, in the sized parts list, and in a plain-English build pack that explains the reasoning behind every choice. No account, no email — about a minute to a complete, validated design.
Once you have more than a couple of connections per polarity, yes. It keeps the battery terminals uncluttered and every joint accessible — which is both safer and required by good practice.
It must be rated for the total current passing through it. Wattonomy sizes the system current so you can match a busbar with enough headroom.
It takes about a minute. No account, no email.