SUEX XJ VR DPV Battery Cell Replacement (SoH <50%)

My client the owner of an old second hand diver propulsion vehicle of SUEX brand XJVR model.

I've been asked to replace the battery pack with new cells. Because this battery deplete faster than other group members, and he lacks in propulsion speed so he lags behind.

He spent in DPV 2000 Eur already for the second hand vehicle, so extra 1400 Eur for new battery is out of question.

New cells and materials cost 150eur and the work is added on top 100%, which makes total 300eur.

This is a less painful liability for an inspected and carefully reassembled battery by an electronics engineer experienced with these cell types and assemblies.

Repairability is fairly easy, only time consuming to weld all the batteries.

Full Picture Album of the process Google Photos

Extra precaution: Experience required to work with energized cells. Fire hazard. Risk of locking the PCB logic.

Tools:

1. M4 nut driver thin barrel that fits to 9.9mm counterbore (I didn't have so I 3D print it in PETG)
2. SPOT WELDER - I use battery powered pedal operated 2 copper electrodes from AliExpress (Ship from EU, ship from China)
3. Some contacts for output connector I used 2mm copper rods for spot welder

Materials:

1. 56 cells to replace (in my case RcShop.lt In Lithuania LG MJ1 3500mAh 10A INR18650 cost 125eur or AliExpress 2.333eur/pcs ship from EU)
2. Nickel strip for cell spot welding 8mm x 0.2mm

SUEX DPV battery view and a printed custom nut driver to compart in 9.9mm counterbore

After removing the battery inspect it and find fastened M4 nuts on each flange lid.

The flanges are fastened with M4 rods axially. On far side nuts are press fitted and on near side - service lid the nuts are fastened deep in D9.9x6 mm counterbore.

Use yours thin barrel nut driver to unfasten the flange/lid.

For the last nut use an extender, if you printed my tool :D

Place the battery on a flat sturdy podium/box, (I used paper cylinders from used spools of 3d plastic)

Carefully start detaching the lid from the barrel cylinder, it is hard and it resists opening.

I used thick screw driver to leverage grip inserted in countersunk holes of the flange used for mounting the battery inside the DPV.

The flange has O-rings between each contacting part, don't loose them.

The cylinder has a wide o-ring seal, and each spacer rod has a smaller o-ring interfacing the flanges.

The flange is a little bit stuck to battery with foam adhesive tape, so detach slowly, while inspecting the movement of guts.

After removing flange you may notice the machined interfaced underside of the flange with some o-rings sticked, where plastic spacers pushed.

Carefully extract each side from the barrel/cylinder cables are in the way.

The cylinder is metal, so it is important to prevent contact with battery welded contacts or PCB

Alse the far side lid has an M12 interface for diagnostic tool, as it is an open wire cable, detach the connector from PCB, to loosen the far side flange.

Inspect the guts and engineering solutions made by manufacturer. In this case the battery is repairable fairly easy. by simply inserting 18650 cells in simple ABS brackets evenly spaced in square format.

Visual Inspection

1. Inspect visually for corrosion and quality of PCB and Cell welded spots, soldered wires.

No corrosion marks, no cracks, no PCB burns

1. Notice configuration of number of cells:

7 in series 8 in parallel, 7S8P configuration.

Multimeter voltage measurements

1. Take a multimeter to inspect each cell group in series.

In my case I received fully charged battery and every cell group was almost 4.2V so a discharger is required for further inspection test.

Discharge Analyzer Energy Measurements

1. Connect a discharger analyzer capable to drain 5A, at 30V 150W (7S * 4.2V = 29.4V)

After 2 hours of discharge test, BMS started to cut-off protection and after some rest kicks-in again.

The moment this happen cell group #7, most positive side at positive battery terminal has reached cut-off voltage 3.0V, while other cell groups had left 3.4V under load.

Conclusion

1. SoC < 50% 250Wh of 575Wh original make.
2. Cells need to be replaced