Cells dead after two years without charging — repairing a Xiluopu scooter Li-ion battery

A Xiluopu scooter’s 48V21Ah Li-ion pack is dead after two-plus years without charging (green light stays on, won’t charge; opened up it smells of electrolyte and the cells are corroded through), so it is rebuilt as 13S4P EVE 18650 2.5Ah = 48V10Ah: fish paper, alternating + / − rows in a jig, no holder with an epoxy board between each series group, 0.2 nickel-plated steel strip welded on both faces watching for missed or loose welds, strapping tape wrap, harness soldered to each group’s tab, BMS fitted and wired, awaiting the charge / discharge test

A Xiluopu scooter Li-ion pack sat for over two years without charging; on the charger the green light stays on and it won’t charge; after two years unused the chance of waking it is very small, most likely dead; label says 48V 21Ah; opening the epoxy board releases a strong sour electrolyte smell, many cells are corroded through by leaked electrolyte, 100% not worth repairing. The customer decides on a rebuild: the scooter is only for getting around and doesn’t need that much capacity, 10Ah is cheaper; new EVE 18650 cells at 2.5Ah each, 13 series × 4 parallel = 48V 10Ah. The cells, with fish paper on, are laid into the jig in 13S4P order, one row positive-up, the next negative-up; the scooter case has no room for holders, so it is a holder-less design with an epoxy board between each series group for insulation; 0.2 thick nickel-plated steel strip spot-welded, the welder set to a suitable current, every cell welded, watch for missed or loose welds, weld both faces, leave the main + and − out. After welding, wrap several turns of strapping tape so it becomes a solid block that won’t come apart under vibration. Fish paper where the harness runs and where the BMS sits; the BMS harness is soldered in order to each group’s tab; the BMS is fitted and the + / − power leads connected; assembly done, only a charge / discharge test to pass and it’s finished. Comments: with alternating rows do the + and − have to be on the two sides; the positive lead is too long, should be thicker (2); how much for a pack (many); how much for 48V20A; do you sell batteries; address.

Outcome

Steps8 steps · click a frame to jump

1. 
   1. Diagnosis: two years unchanged, green light stays on and won’t charge, little chance of waking it

   The Xiluopu scooter Li-ion pack sat for over two years without charging; the charger’s green light staying on means it won’t charge; after two years unused the chance of waking it is very small, most likely dead.

   00:13 – 00:40
2. 
   2. Opened up: 48V21Ah label, sour electrolyte smell, cells corroded through, not worth repairing

   Label 48V 21Ah; removing the epoxy board releases a strong sour electrolyte smell; many cells are corroded through by leaked electrolyte; 100% not worth repairing.

   00:40 – 01:10
3. 
   3. Plan: EVE 18650 2.5Ah, 13S4P = 48V10Ah

   Getting around doesn’t need big capacity, 10Ah is cheaper; new EVE 18650 cells at 2.5Ah each; 13 series × 4 parallel, 48V10Ah.

   01:09 – 01:35
4. 
   4. Fish paper; alternating + / − rows in the jig; no holders, epoxy board between groups

   Cells with fish paper on go into the jig in 13S4P order, one row positive-up, the next negative-up; the case has no room for holders, so a holder-less design; an epoxy board between each series group for insulation.

   01:36 – 02:04
5. 
   5. 0.2 nickel-plated steel strip, both faces, watch for missed / loose welds, leave the main + and −

   0.2 thick nickel-plated steel strip spot-welded; welder set to a suitable current; every cell welded; watch for missed and loose welds; weld both faces; leave the main + and − out.

   02:05 – 02:27
6. 
   6. Wrap with strapping tape into one block

   After welding, wrap several turns of strapping tape so it becomes a solid block that won’t come apart under vibration.

   02:37 – 02:51
7. 
   7. Fish paper under the harness, harness soldered to each group’s tab, BMS fitted and power leads connected

   Fish paper where the harness runs and where the BMS sits; the BMS harness is soldered in order to each group’s tab; fit the BMS and connect the + / − power leads.

   02:57 – 03:55
8. 
   8. Assembly done, awaiting the charge / discharge test

   The assembly work is done; only a charge / discharge test to pass and it’s finished.

   04:04 – 04:15

Bill of materials

Creator’s tips

• A Li-ion pack left uncharged for two-plus years is most likely dead; a sour electrolyte smell plus corrosion means it isn’t worth repairing 00:38
• When the case has no room for holders, go holder-less — epoxy board between groups and strapping tape around the whole block 01:50
• When welding, just watch for missed and loose welds, and weld both faces 02:18
• For a runabout you can drop capacity to cut cost (21Ah → 10Ah) 01:09

Pitfalls

• Long spells without charging corrode the cells and kill the pack 00:55
• Comment: the positive lead is too long and needs to be thicker

Li-ion safety

• Corroded cells with a sour electrolyte leak must not be used again 00:55
• Epoxy board between groups for insulation, fish paper under the harness 01:50

Quotes