Why does one parallel battery charge more slowly than the others?

What you will see

• One battery consistently shows a lower charge percentage.
• Individual battery charging currents differ, where those readings are available.
• One unit appears inactive while others charge.
• The difference began after an additional battery was installed.

Why it happens

In parallel banks, differences in resistance through cables and connections can affect how charging current is shared. An installer should assess the complete current path and the manufacturer’s approved connection arrangement.

Battery status also matters. Managed systems communicate charging limits and operating information, and a unit that is restricted or not correctly recognised needs investigation. A group charge percentage does not, by itself, establish that every installed battery is participating normally.

Displayed state of charge is an estimate. A difference between readings can involve estimation or commissioning issues as well as a real difference in stored energy. Manufacturer guidance for some modular systems specifically addresses charge alignment when adding modules.

This makes the history valuable. Tell us whether the batteries were installed together, whether one has been replaced, and whether the readings used to remain closer. The review should establish what changed before recommending a replacement.

Diagram

Same bank, different readings

Battery 1Battery 2Battery 3

Possible reasons:

Cable and connection resistanceUnit not recognisedCharge limit on one unitSOC estimateAdded later

What you can check yourself

• Photograph the visible indicators on each battery at the same time.
• Label your notes by battery position so the same unit can be followed consistently.
• Save individual readings from the normal app if they are available.
• Record any battery warnings and whether the displayed unit count matches the installed count, where shown.
• Note installation dates and whether the difference appears during charging, discharge or both.
• For a Dyness, Pylontech, Soluna or other bank, send the exact model labels. The brand name alone does not identify the connection or expansion rules.

What not to do

• Do not disconnect one battery to “test it,” swap power leads, tighten live terminals or alter communication switches.
• Do not try to equalise units using an external charger or a procedure intended for another battery type.

When to call us

• Arrange a check if a battery remains inactive, an alarm appears, or the difference continues across normal operating cycles. Request a commissioning review if the issue began immediately after expansion or replacement.

Battery banks in Faisalabad and Lahore

Our Faisalabad and Lahore teams review the complete current path, communication and expansion history before recommending a replacement.

Send us

Every battery model, the inverter model, unit count, simultaneous screenshots, expansion history, and your city and area.