#Lithium battery repair training

The customer's old case is only 130×370, so I measured three times before I dared to cut anything. 13S6P, 0.2 nickel-plated strip, UF20B at gear 38 — watching the welds light up one by one is seriously addictive. Halfway through, the welding pens touched and blew a hole right through one cell. Swapped it out and started over — newbies, remember this: position first, then press. Don't rush. BMS goes in tomorrow, it goes back to the customer the day after. Will report back.

I just want to ask, which courier do your fans ship with?

Roughly how much to build a 48V 30A, boss?

Are you in Shenyang?

How much is one of these cells????

How much to re-cell this?

Is 15Ah enough to get work done?

How much is this welder of yours?

A follower from out of town sent in a 48V Li-ion e-bike battery, label says 48V 15Ah Panasonic cells, made 2023-12; it feels feather-light in the hand, clearly not 15Ah, range is very short and nowhere near the kilometres the seller promised. Off with the top cover: the cells only take up a little space in the middle, the rest is foam padding, the block is very small; inside it’s 18650s, 13S3P, the wrappers carry no brand or capacity info — typical knock-off cells, you can imagine the range; this battery is worth nothing. Rebuild as 15Ah: brand-new EVE 18650s at 2.5Ah each, 6P13S; place them in the holder alternating + up / − up, lay one row first as the reference, mind the orientation and don’t get it wrong; snap the top holder on to make one block; the connecting material is 0.2-thick nickel-plated steel strip cut to the needed lengths; the welder is just an ordinary capacitor spot welder — 18650s don’t need much current; 4 welds per cell to guarantee current-carrying strength; weld the parallel and series links in order, then check the whole block for wrong or missed welds; fit the BMS, charge and discharge test, no problems and it’s done. Warning: when buying a battery, any pack whose cells are labelled CATL, Panasonic and the like is fake. Comments (343): how much for a 48V30A build (2); 12C 25P cell config is overkill, 5C is enough (2, doesn’t match this video); selling fakes is a crime, jail (1); which courier did you use (1); how much for 48V25A; how much to rebuild a Sunra; you can tell it’s only a few Ah just by looking.

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.

Opens with the customer: the battery hasn’t lasted well since 2024, used to charge for three hours, now goes green the moment it’s plugged in. Label says 48V 15Ah, made 2024-09; the problem is it won’t charge or discharge. Opened up: cylindrical 18650s; the case says 15Ah, but the cells are 2.5 each in 4P, really 10Ah; clearly salvaged old cells used a second time, many already leaking; very crude workmanship; he decides to scrap the cells and rebuild with brand-new ones; the only usable part of the old pack is the BMS, removed for reuse. Rebuild: 18650 at 2.5Ah each, 48V10Ah needs 13S4P, 52 cells, brand-new EVE; laid into the holder one group positive-up, next negative-up; series raises voltage, then 4P adds capacity. Welding uses 0.2 nickel-plated steel strip on a capacitor spot welder, settings on the screen (preheat auto 0.05ms, interval 20ms, gear 29, trigger 0.6s, continuous); the process is simple as long as nothing is missed; check for missed or wrong welds afterwards. Fit the BMS, usually on the negative side; pre-cut insulating paper where the sense leads run; tidy the ribbon and weld it to each group’s tab in order — the order must not be wrong; the sense leads monitor each group’s voltage and cut the BMS circuit if it goes too high or too low; to avoid mistakes, after each weld the lead order is checked on a test board before connecting the BMS. Finally the + and − power leads go on, a proper charge/discharge test (49.53V 4.92A), then insulation, back into the case, done. 16 comments: are the EVE 25Ps genuine (print and barcode misaligned); how much for a pack (1); how much for a 48V50Ah for a ride-share bike; how much per cell; are you in Shenyang; the original didn’t even have a holder; what BMS is that small.

A customer sent in a 48V e-bike battery case whose cells were dead. The creator measured the inside (130 × 370), worked out that 13S6P would fit, and chose EVE 2.5Ah 18650s — 78 cells for 48V 15Ah. Cells go into the holder alternating positive-up / negative-up (parallel across, series down), get spot-welded into one block with 0.2mm nickel-plated steel strip on both faces, with the main positive and negative brought out separately. The pack is wrapped in strapping tape, the BMS is fitted with its balance leads soldered to each series group in order, the input/output leads are connected, and a charge/discharge test (49.14V / 6.50A on screen) is run before delivery.