Methodology

Scope: 12 V systems with LiFePO4 batteries in parallel. Verdicts compare published specs with the arithmetic below. Nothing here sizes wire, fuses, or breakers; see safety.

Energy

• Bank Wh = capacity (Ah) × batteries in parallel × 12.8 V (4 cells × 3.2 V) [C].
• Usable Wh = bank Wh × (1 − reserve). The default reserve is 20%, so 80% is planned as usable; the planner lets you change it [H].
• Daily use (battery side) = DC loads (W × hours × duty cycle) + AC loads ÷ inverter efficiency + inverter idle draw × hours on. Inverter efficiency is the maker's figure, or 88% when none is published [H].
• Daily charging = solar W (capped at controller output A × 14.2 V) × peak sun hours × 0.75 [H] + DC-DC output A × 14.2 V × driving hours [H] + converter A × 14.2 V × shore hours [H].
• Days of autonomy = usable Wh ÷ (daily use − daily charging); unlimited when charging covers use.
• Energy verdict: works if days ≥ target × 1.2; tight if days ≥ target; otherwise no [H].

Component checks

• Inverter vs battery BMS: DC amps = inverter W ÷ efficiency ÷ 12 V [H]. Works at or below 80% of the combined published BMS continuous rating, tight up to 100%, no above it [H].
• Charger current: charger A vs the published max charge current × batteries in parallel.
• Charge voltage: the converter must list a lithium mode, and its published lithium charge voltage must sit inside the battery's published charge-voltage range. A lithium mode with no voltage to compare shows as tight, not works.
• Combined charging: charger amps from shore, alternator and solar are capped at the bank's published max charge current; below the minimum charging temperature with no heater, charging counts as zero.
• Box fit: the battery maker's published L × W × H vs the box (or BCI's maximum group dimensions). Differences of 1 mm or less count as equal; under 10 mm to spare is tight [H].
• Cold charging: the coldest expected battery temperature vs the published minimum charge temperature; a published self-heater turns no into tight.
• DC-DC alternator draw (shown, not judged) = output A × 14.2 V ÷ efficiency ÷ 13.5 V; efficiency is the maker's figure or 90% [H].
• A check with a missing spec shows as not published, never as a pass, and it keeps the overall verdict below works. The worst check sets the overall verdict.
• Each check is explained, with the full list, on the checks page.

Provenance labels

• maker spec: a value the maker publishes, with a verbatim quote, the source, and the date we read it.
• calculated: our formula applied to spec values, with the assumptions above.
• third-party test: a result published by a reviewer or lab, quoted as published with its method and date.

We do not test products and hold no electrical certifications. Verdicts compare published specs; they are not installation advice.

Wiring and fusing

Where a maker states its own fuse or cable requirement, we quote it word for word with the source. We never add our own wire size or fuse advice. For charging from the vehicle, use a DC-DC charger installed per the maker's instructions.

Sources and refresh

Each value is collected from a primary source with a quote, then checked again in an independent second pass. Unpublished values show as not published.