An RV upfitter has received four 12V 100Ah LiFePO4 batteries for a parallel bank. With a multimeter, the resting voltages differ by a few tenths of a volt.
Don’t connect them straight away. Small differences on arrival are normal, because batteries are usually shipped part-charged. But paralleling batteries at different states of charge causes current to flow between them and leaves the bank out of balance from the start. Charge each battery fully on its own with a LiFePO4 charger, let them rest, check they match, and only then connect them.
Why resting voltage needs care
LiFePO4 voltage is very flat across most of its state of charge. A difference of a few tenths of a volt at rest can mean a large difference in stored energy. When batteries at different states are paralleled, the fuller battery charges the emptier one, and the current is limited only by the cable resistance and the BMS.
Steps before paralleling
- Check every battery is the same model and capacity. For example, Redway’s 12V 100Ah ULTRA lists up to 4 in parallel and the 12V 100Ah Slim up to 6.
- Charge each battery separately to full with a charger set to the datasheet’s charge voltage (14.6V on these 12V models), until the charger finishes.
- Let them rest, ideally for several hours, then measure each one. They should now read very close to each other.
- Connect with equal-length cables. Take the main positive and negative from opposite ends of the bank, and fit fuses sized as in our cable and fuse guide.
When a difference is worth reporting
- One battery won’t reach full charge, or its BMS stops charging early.
- One battery shows a much lower voltage than the rest, or near the BMS cut-off (10V on the 12V ULTRA).
- Bluetooth data, if fitted, shows a large spread between cells within one battery.
Record the serial numbers and readings and contact the supplier before you install.
Risk limits
Don’t parallel mixed models or batteries of different ages. Don’t connect a battery that is at or below cut-off to a full one. Wiring in series has separate requirements, so check whether the datasheet allows it. Our parallel and series wiring guide covers layouts.
Additional perspectives
Ask the supplier what state of charge batteries are shipped at and whether serials in one order come from the same production batch. Write an incoming check into your receiving process: record serial, voltage on arrival and date. That turns “arrived at different voltages” from a dispute into data.
Redway Tech Editorial Team – Procurement perspective
Plan the extra charging time into the build schedule. Charging four 100Ah batteries one after another takes time, and a bench charger matched to LiFePO4 is worth having in the workshop. Label each battery with its position in the bank so any later fault can be traced back to the receiving record.
Redway Tech Editorial Team – Installation perspective
After commissioning, compare the batteries now and then. If they have Bluetooth (Redway lists it as an option), check each one’s state of charge. If not, briefly disconnect and compare resting voltages after a full charge. A battery that drifts consistently is the one to investigate, rather than the whole bank.
Redway Tech Editorial Team – Maintenance perspective
Specifications are taken from Redway product pages as of October 2026. Where a figure isn’t published, this article says so. Confirm current specifications for your model with Redway before ordering. This article is general guidance, not a site-specific engineering assessment.
Related products
- 12V 100Ah Lithium LiFePO4 Battery (ULTRA)
- 12V 100Ah Lithium Battery Manufacturer
- 12V 200Ah Lithium LiFePO4 Battery (ULTRA)
- 24V 100Ah Lithium LiFePO4 Battery (ULTRA)
Related topics
- Battery Bank Configuration
- Battery Series, Parallel & System Sizing
- 12V LiFePO4 Battery Systems
- Battery Series, Parallel & Bank Design
- Marine Battery Chargers, Tenders & Banks
- Golf Cart Battery Installation, Wiring & Conversion
- Rack Battery Installation, Wiring & Safety
- RV Battery Installation, Wiring & Inverter
- Parallel Configurations
- BMS Installation & Wiring
Continue learning
LiFePO4 Technology
Related reading
