FAQ
TL;DR: 65 % of 0 V 18650 cells can be revived and reused [Elektroda, remzibi, post #21584666] “Thermal imaging catches issues months early” [Elektroda, remzibi, post #21565641] A DIY 14 S/48 V rack hit 24 kWh for ~PLN 2 200 in balance-of-system costs [Elektroda, remzibi, post #21278634]
Why it matters: Home energy storage built from reclaimed cells can halve bills yet demands strict testing, balancing and fire-safety discipline.
Quick Facts
• Target pack: 14 S × 6 P × 40 strings → 24 kWh, 48 V nominal [Elektroda, remzibi, post #21276258]
• Average working current: 250–350 mA per cell; peaks to 600 mA [Elektroda, remzibi, post #21280164]
• Operating window: 3.3 V–4.13 V/cell; BMS hard cut-off 2.9 V/4.2 V [Elektroda, remzibi, post #21277727]
• Materials (excluding cells): ≈ PLN 2 200 including JK-BMS 150 A, welder, wiring [Elektroda, remzibi, post #21278634]
• Failure rate: ~35 % of tested laptop or e-bike cells rejected for IR, self-discharge or capacity [Elektroda, remzibi, post #21278484]
What configuration gives the 24 kWh capacity?
The builder uses 14 series groups, each eventually holding 40 parallel sticks of 6 × 18650 cells (14 S × 240 P ≈ 3 240 cells). At 3.6 Ah median per cell this totals about 24 kWh at 48 V nominal [Elektroda, remzibi, post #21276258]
How are second-life cells screened before welding?
- Boost 0 V cells to 2.8 V at 50-100 mA.
- Rest 24 h; discard if voltage drops.
- Charge 700 mA CC/CV, monitor; reject if >40 °C.
- Measure capacity & internal resistance; age one month and re-measure.
- Only matched cells go into strings [Elektroda, remzibi, post #21565641]
What share of scrap cells survive the full test?
About 65 % of zero-volt cells and roughly 50–70 % of e-bike or laptop pulls pass all checks; the rest become torch or power-bank donors or go to recycling [Elektroda, remzibi, #21278484; #21565641].
Which brands fail most often?
“Unquestionably the worst crap are LG Chem” due to high self-discharge and capacity loss, according to the tester [Elektroda, remzibi, post #21585599]
Why were some plastic cell holders replaced?
Unbranded Chinese sockets began cracking after a few months; printed, numbered variants remained intact. All suspect frames were swapped during a two-week rebuild [Elektroda, remzibi, post #21565641]
How is balancing handled?
A JK-BMS 20 S 150 A with 1 A active balancer keeps cell groups within 0.01 V; settings start balancing when ΔV > 0.02 V [Elektroda, remzibi, post #21277727]
What thermal-safety methods are used?
Three-degree hotspots are detected during weekly scans with a handheld infrared camera; suspect cells are replaced live. A cell leaked electrolyte yet was caught months before failure [Elektroda, remzibi, post #21565641]
Can the rack deliver full inverter power?
Yes. Short tests at 4.5 kW showed stable voltage and temperature, implying inverter efficiency around 93 % at 48 V, though no formal load-curve was recorded [Elektroda, remzibi, post #21596531]
What happens if one 18650 shorts in a parallel stick?
Each cell retains its own CID rupture disc. A sudden short triggers the internal fuse; worst-case the 4 A external fuse on the stick opens before thermal runaway spreads [Elektroda, remzibi, post #21276258]
Edge case: charging in winter?
The rack sits in a concrete room that never drops below 15 °C, avoiding lithium plating that can occur below 5 °C [Elektroda, remzibi, post #21281453]
How much did the storage save?
By May 2025 the system paid back its entire cash outlay and now nets a monthly surplus, thanks to two-day autonomy during cloudy spells and vertical 4.7 kW PV panels [Elektroda, remzibi, post #21565641]
Is an external shed safer?
Yes. Forums note reduced gas-inhalation and fire risk when lithium packs sit in a detached, temperature-controlled enclosure, though heating may be needed to stay above 10 °C [Elektroda, cefaloid, post #21283526]
How does this compare with LiFePO₄?
LiFePO₄ offers higher cycle life and lower fire risk but costs 3-4 × more per recovered kilowatt-hour. For zero-cost reclaimed 18650s, Li-ion remains the cheapest kWh despite extra monitoring [“Battery Cost Survey”, 2024].
Quick how-to: adding a new parallel stick online?
- Charge new 6-cell stick to 4.13 V.
- Verify ΔV ≤ 0.02 V to existing row.
- Bolt & weld into rack; BMS auto-learns capacity [Elektroda, remzibi, post #21296653]
