Solar guide

Solar & battery system troubleshooting

Diagnose solar and house-bank problems by chemistry — LiFePO4 vs AGM, charge-controller stages, array faults, and when a Victron Professional install beats guesswork.

Active corridor: Montana · Wyoming · Idaho · Washington — case-by-case beyond.

Field notes

This is the page to start on for battery-related symptoms — chemistry basics, charging, maintenance, and field troubleshooting. Brand-specific fault text: Victron MultiPlus / Quattro / SmartSolar for Victron stacks; Progressive Dynamics / WFCO / Xantrex on their fault index when that is your chassis. United Mobile RV is a Victron Professional Certified Installer — we design and diagnose these systems as electrical work, not gadget swaps.

Who this is for

Right place if you

Bank will not hold a charge. Solar underperforms after a perfect sunny day. Inverter shuts down under load. You mixed chemistries or charger profiles and need honesty before buying another battery.

Maybe not yet if

You only need a Victron alarm decoded — confirm the exact text in VictronConnect, then open the Victron fault-code guide. You only need shore-power / pedestal diagnostics — start on electrical troubleshooting.

Battery chemistry: why it changes everything

The single biggest mistake in RV battery systems is treating lithium (LiFePO4), AGM, and flooded lead-acid as interchangeable. They need different charge voltages, discharge habits, and storage practices — a charger set for one chemistry will damage another over time.

Lithium (LiFePO4)

Deep-cycle friendly with a working BMS. Does not want lead-acid float habits. Cold charge inhibit near freezing is common — confirm your battery/BMS manual (many inhibit around 0 °C / 32 °F; heated packs differ). Do not invent a universal cutoff.

AGM

Sealed, no watering, but repeated discharge below about 50% shortens life. Needs correct absorb/float — not a lithium profile bolted on.

Flooded lead-acid

Needs watering and occasional equalization per manufacturer. Most abuse-tolerant to casual DIY — still easy to sulfate in storage.

Mixed banks

Paralleling unlike chemistries or ages is how mystery drains and charger fights start. Fix topology before buying another bigger battery.

Battery not holding a charge

Lithium: BMS protection from deep discharge, over-temperature, or cell imbalance is far more common than a truly dead pack
Lead-acid / AGM: sulfation from repeated deep discharge or long storage without a maintainer
Parasitic draw: something left on, inverter standby, or aftermarket always-hot loads
Charger / converter: wrong profile, failed stage sensing, or open internal fuse
Cable & lugs: voltage looks fine at rest at the battery and collapses at the inverter under load

Capacity testing: is the battery actually bad?

Resting voltage alone does not tell you much — a battery can read a normal resting voltage and still fail to deliver capacity under load. A proper capacity test (controlled discharge with a known load, or manufacturer-approved tester workflow) is the only way to know. Replace on data, not on “it looks old.”

Storage & maintenance charging

Lithium storage

Store around 50–60% SoC — not 100% for months. Confirm cold storage rules in your BMS manual.

Lead-acid / AGM storage

Store fully charged on a maintenance/float charger sized for the bank. A “full” battery left alone all winter often returns sulfated.

Solar not charging or underperforming

Shading & array

Partial shading from a vent, A/C, or antenna can drop output far more than the shaded area suggests — especially on non-optimized strings.

Controller profile

Wrong battery type, wrong system voltage, or remote/BMS control disabling charge. Confirm settings in the app or display before condemning panels.

Wiring & fusing

High resistance MC4s, undersized cable, open fuses, and loose lugs impersonate “bad solar.”

Cold Voc risk

Cold mornings raise panel Voc — string design must stay under the MPPT max. Overvoltage errors are often design, not a failed controller.

MPPT vs PWM basics: MPPT vs PWM. Off-grid budgeting: power budget. Buying lithium: lithium buying guide.

Inverter faults & shutdowns

Low-voltage shutdown

Bank sagged under load — undersized cabling, high resistance lugs, BMS load disconnect, or a bank smaller than the surge.

Overload shutdown

Connected load or inrush exceeded capability — microwave + induction + compressor stories are classic.

Overtemp

Hot bay, blocked airflow, failed fan. Derate expectations for summer mountain climbs with continuous loads.

Ripple / connection quality

Loose DC lugs beat board replacement more often than owners want to hear. Meter at the inverter under load.

DIY vs book UMRT

Reasonable DIY

Clean terminals, verify app settings against the battery manual, note shade patterns, photograph VictronConnect / charger screens for Prefer Text triage.

Book us when

You need capacity testing, cable/fuse redesign, Victron Professional integration, or a system that has never been configured correctly since install. Corridor: MT · WY · ID · WA.

FAQ

Solar is zero on a sunny day?

Confirm array Voc/Vmp at the controller, breaker/fuse state, and whether BMS/GX remote control disabled charging. Cold-charge inhibit looks like “MPPT broken.”

Can I charge lithium with my stock converter?

Only if the profile matches the battery requirements. Many stock converters are lead-acid-centric and will mistreat LiFePO4.

Do I need a bigger inverter?

Maybe — or you need honest cable, surge math, and bank capacity first. Peak stickers are not continuous ratings.

Where do Victron manuals live?

Official Victron live wiki and manuals hub only. Software twin: umrt-software VictronConnect troubleshoot.

Book a Service Prefer Text All guides

Pricing teaser

Trip fee $75 within 30 miles, then $1.50/mi each way. Labor ~$150/hr (1-hour minimum, billed in 30-minute increments). Diagnostic $175 applied toward repair if you proceed.

Credentials (text): Victron Professional Certified Installer · weBoost Authorized Installer · Peplink Certified Associate · Dometic Professional Certified. Starlink = installs only (not a certified partner title).