Used / Second-Hand LiFePO4 Batteries: Worth It?
Used LiFePO4 batteries are increasingly available as the first wave of van builds gets upgraded or sold. They can be genuine value — or expensive problems. Here's how to evaluate them.
Where used LiFePO4 batteries come from
Van build upgrades: Someone who started with a 100Ah battery is now putting in 200Ah. Their old battery is 2 years old with 500–700 cycles.
Failed van builds: The project got sold. The battery may be nearly new with under 100 cycles.
RV dealerships / campground upgrades: Campgrounds and rental fleets upgrading their house batteries.
EV industry salvage: Damaged or recalled EV packs are sometimes broken down into individual cells and repackaged. These are high-risk — cell provenance is unclear.
Online marketplaces: Facebook Marketplace, Craigslist, eBay. Condition varies wildly.
How to evaluate a used LiFePO4 battery
Visual inspection
- Case: Any cracks, deformation, or swelling? A bulging case indicates cell issues — don't buy.
- Terminals: Corrosion is common but usually cleanable. Heavy corrosion or green/white powder at the terminals indicates moisture exposure.
- BMS connector: Should be undamaged and firmly seated.
Electrical test
Resting voltage check: A good LiFePO4 should hold 13.0–13.4V at rest (no load, no charge). Below 12.5V suggests either deep discharge or cell imbalance.
Charge to full: Use a known LiFePO4 charger set to 14.4V. Charge until current tapers to near zero. Note: if the BMS is in over-discharge protection mode from a very low state, the charger may not "see" the battery — use a recovery mode charger.
Capacity test: After full charge, discharge with a known load (a 60W light bulb = 5A at 12V). Count amp-hours until BMS trips. Compare to rated capacity. A healthy 100Ah battery delivers 80Ah+ at this rate.
Internal resistance test: A battery load tester or dedicated internal resistance meter shows cell health. Elevated internal resistance (significantly above factory spec) indicates cell degradation.
Questions to ask the seller
- How many cycles? (Rough estimate is fine — sellers often don't know exactly)
- Was it ever charged below freezing?
- Has the BMS ever tripped unexpectedly?
- What was it used for? (RV/van = well-understood use; unknown = more risk)
Pricing guidelines
A used LiFePO4 battery is worth buying at approximately:
- Under 500 cycles, verified capacity >90%: 60–70% of new price
- 500–1,500 cycles, verified capacity 85–90%: 40–55% of new price
- 1,500+ cycles, capacity unknown: Under 30% of new price, or pass
Given that new LiTime 100Ah batteries are ~$280, paying more than $200 for an unverified used battery is hard to justify. If you can get a Battle Born with under 500 cycles and verified capacity for $400–$500, that's a clear win at half of new price.