Busbar or daisy chain, and why the first battery ages fastest

Wire four batteries in parallel by hopping from one to the next, and they will not share current evenly. The pack closest to the inverter sees the shortest path, the least resistance, and the largest share of every charge and discharge.

The difference is small per cycle and cumulative over years. The hardest working pack ages faster, its capacity drops first, and a bank that was balanced on day one develops a weak member that drags the whole string.

Two arrangements that fix it

A busbar gives every battery its own identical run to a common point. Same cable length, same lug, same torque, so the current divides by battery impedance rather than by wiring luck. It costs more in cable and it is the arrangement every manufacturer diagram shows.

Diagonal wiring is the cheaper approximation: take the positive from one end of the string and the negative from the other end, so the total path length through each battery comes out roughly equal. It is a real improvement over hopping and it is not as good as a busbar once you go past three or four packs.

The part people skip

Cables must match in length as well as gauge. A pair of runs that are the same size but different lengths reintroduces the imbalance the busbar removed. Cut them together, crimp them the same way, and torque every lug to the published figure.

Torque matters more than it sounds. A loose lug heats under load, heat raises resistance, higher resistance produces more heat, and that loop ends at a melted terminal. Most manufacturers publish a torque value. Some do not, which is its own problem and one this site tracks rather than guesses at.

Related pages on this site

• Batteries and their parallel limits
• EG4 LifePower4, the pack most often wired in fours
• Inverters and the charge current a bank has to absorb