RV OWNER’S FIELD GUIDE · SOLAR & POWER
Lithium vs. AGM vs. Lead-Acid, Compared
The sticker price isn’t the real comparison. Cost per usable cycle is.
| Flooded Lead-Acid | AGM | LiFePO4 | |
|---|---|---|---|
| Usable capacity | ~50% | ~50% | ~90–100% |
| Cycle life (to 50% DoD) | 300–500 | 400–700 | 2,000–5,000+ |
| Weight (per 100Ah-equiv usable) | Heaviest | Heavy | ~half of AGM |
| Charges below freezing? | Yes, reduced capacity | Yes, reduced capacity | No, without internal heater |
| Maintenance | Water levels, terminals | Terminals only | None |
Why Lithium Usually Wins on Cost Per Cycle
A lead-acid or AGM bank you can only draw down to 50% without shortening its life; lithium you can draw to near-empty repeatedly. Combined with 4–10x the cycle life, the effective cost per usable amp-hour over the battery’s life is usually lower for lithium even though the upfront price is higher — the breakeven point is typically somewhere in year two or three of regular use.
When AGM or Flooded Still Makes Sense
A rig that sits in storage most of the year, sees light use, or where upfront cost matters more than long-term efficiency — AGM remains a reasonable, lower-cost choice. It’s also more forgiving in extreme cold since it doesn’t have a hard charge cutoff below freezing the way lithium does without a heated option. See our BMS guide for how that cutoff actually works.