A motorhome owner switched to LiFePO4. Plugged into shore power overnight, the monitor still shows 85–95% in the morning and the charge voltage at the battery seems low.
Usually it’s the charging setup, not the battery. Common causes are a converter that isn’t charging in a lithium mode, voltage drop in thin or long cables, a monitor reading voltage rather than counting current (or a shunt in the wrong place), and a bank that hasn’t completed a full charge for a while. Check these before suspecting the cells.
Why converters stall
Many older converters were designed for lead-acid and hold around 13.6V, which is closer to a float level for a 12V LiFePO4 battery. At that voltage a LiFePO4 bank charges very slowly near the top. Redway’s 12V ULTRA and 12V 200Ah ULTRA specify a 14.6V charge voltage. Follow your battery’s datasheet for absorption and float settings.
Step-by-step check
- Charger mode: confirm the converter or charger has a LiFePO4 profile and that it’s selected.
- Voltage at both ends: measure at the converter terminals and at the battery terminals while charging. A big difference means voltage drop. Some chargers then switch to float early.
- Monitor setup: make sure the shunt sits between the battery negative and everything else, so all charge and load current passes through it. Set the correct capacity, and resync to 100% after a confirmed full charge.
- Full-charge evidence: charge until current tapers right down at the datasheet charge voltage. If the battery has Bluetooth, check that its own state of charge reads 100%.
- Battery side: if one battery in a parallel bank behaves differently, check it on its own.
Conditions
Cold weather matters. Redway’s 12V ULTRA lists a 0°C minimum charging temperature, and its BMS may block charging below that. Self-heating is offered as an option. Large DC loads running while plugged in also reduce the current left for the battery.
Risk limits
Don’t set charge voltages above the datasheet. Don’t use desulfation or equalization modes on LiFePO4. Have cable and converter upgrades done to your RV’s electrical standards. See RV Batteries and Charging & Chargers.
Additional perspectives
When upgrading an RV to LiFePO4, budget for the charging side as well as the battery: a converter or charger with a proper LiFePO4 profile, adequate cable gauge and a shunt-based monitor. If the RV is used in cold weather, consider self-heating models, which Redway lists as an option.
Redway Tech Editorial Team – Selection perspective
Don’t chase 100% on the display every day. LiFePO4 doesn’t need to sit full, and many owners deliberately store partly charged. What matters is an occasional confirmed full charge, so the monitor can resync and the cells can balance. If the monitor’s 100% and the battery’s own state of charge disagree, trust the measurement taken through the shunt and recalibrate the display.
Redway Tech Editorial Team – Maintenance perspective
At handover, give the owner the charger profile settings and a voltage-drop reading taken under full charge current. Recording the measured voltage at the converter and at the battery during commissioning saves a service call later, when ‘won’t reach 100%’ is reported.
Redway Tech Editorial Team – Upfitter 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 200Ah Lithium LiFePO4 Battery (ULTRA)
- 12V 100Ah Lithium Battery Manufacturer
- 24V 100Ah Lithium LiFePO4 Battery (ULTRA)
Related topics
- Discharge Curves & Voltage Sag
- Capacity vs Charge Rate Trade-offs
- Voltage Drop & Cable Sizing
- 12V LiFePO4 Battery Systems
- Battery Capacity, Reserve & Cranking Ratings
- Battery Voltage Testing, Charts & Cutoffs
- Lithium Battery Charging, BMS & Pack Design
- Marine & RV Battery Models and Specifications
- Forklift Maintenance & Service Reference
- Forklift Charging Systems & Troubleshooting
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