Introduction: Pro-Grade 12V LiFePO4 Battery Bank: 32-Day Performance, Full Discharge Test, and DIY Monitoring

By
About: Retired engineer

This project documents the build and real-world testing of a 12V 500Ah LiFePO4 battery bank for backup and solar power. My goal: create a high-performance, professionally monitored DIY system, validate rated capacity with a controlled full-cycle test, and establish ongoing health/quality benchmarks using continuous data. This guide details every step—design, cost, wiring, logging, test results, and conclusions—so other builders can replicate, improve, or benchmark their own builds.

Attachments

Supplies

Step 1:

System Layout & Schematic

The bank uses five LiFePO4 cells (LiPULS and Cyclenbatt brands, 100Ah each) wired in parallel, each with its own BMS and fuse for safety. All batteries connect to a copper bus bar with M8 bolts, feeding a 1500W pure sine inverter. System protected by both individual 100A MRBF fuses and a main 300A ANL fuse.

Diagram:

  1. Upload your bus bar schematic and wire layout image or PDF.
  2. Notes:
  3. All connections torqued to spec (20 ft-lbs).
  4. Redundant DC+AC instrumentation (Drok + Shelly; Kill-A-Watt for output).

Test Protocol & Methodology

  1. Hourly/daily voltage monitored using Shelly Uni and Drok monitors.
  2. One full discharge: Batteries run from fully charged (13.65V) to 20% SOC (~12.61V), output measured with Kill-A-Watt and Drok.
  3. Logging included min, max, and average voltages, amp-hours delivered per cycle, and rest periods to track balance and self-discharge.
  4. Batteries disconnected from loads/charger after Nov 3 to isolate idle self-discharge.

Cycle definition:

  1. Full cycle: Complete discharge to ≤20% SOC, then recharge to 100%.
  2. Partial cycle: Smaller SOC swings; discharge/recharge events with ≥0.08V change, but not to deep cutoff.


Step 2:

Results & Critical Findings

  1. Capacity delivered: 397Ah (99.25% of rated capacity) over 10.5 hours, 4.62 kWh AC output.
  2. Self-discharge rate: ≤0.25% SOC/month, measured during 19 idle days (no use or charge).
  3. Pack balance: <0.05V variation over 32 days (no drift detected).
  4. Cycle health: No measurable fade after 1 full cycle and 7 partial cycles; voltage and resistance unchanged.
  5. Thermal performance: Cooler than many comparable DIY builds; negligible heat at tested current.
  6. Economic value: Levelized cost $0.084/kWh (hardware only), highly competitive vs. grid or generator backup.

How to Repeat/Improve This Method

  1. Log voltage daily with smart sensor and amp-hour monitor for each cycle.
  2. Keep load consistent for accurate cycle-to-cycle comparison.
  3. Record pack temperature if possible.
  4. Track resistance and balance for signs of mismatch or aging.
  5. Run at least 50 full cycles for “statistically robust” longevity claims.
  6. Share raw log files with community for peer review.


Step 3:

Conclusion & Invitation


Certification of Deployed System Performance

This test regimen conclusively validates that this specific, deployed system meets all critical performance requirements for its role as residential backup infrastructure. The data certifies the installed site hardware's capacity, efficiency, and stability.

The exceptional cell matching (resting delta <0.05V) observed across mixed battery brands suggests consistent manufacturing tolerances within the sourced batches. However, these results specifically and solely certify the operational reliability of this installed system, providing a validated baseline for its long-term management and serving as a reference design for future replication.

Questions, feedback, and suggestions for improved long-term cycle tracking are welcomed. If you replicate or expand on these tests, share your own cycle logs and voltage data with the DIY community!


See my proven methodology at: colliscope8.gumroad.com/l/AIValidation