Fastkar on the sticker. Inside, one skinny nickel.

Fastkar reach our shop already

Illustrative shop scene and virtual chat.

The Malay kid came into our shop with his shiny Alibaba battery and a face blacker than the heat-shrink.

We asked what happened.

“Battery cut lah.”

Then he put his phone on the bench.

“See what these fellas keep sending me.”

Apparently, before the race, he was the fastkar of the group. His Fiido could fly to JB. His friend’s fixie? Can throw longkang already.

At the start, he gave the throttle one confident twist.

Battery cut.

The fixie went past. Then the rest went past. His promises were still at the starting line with him.

The group chat started before he finished checking the plug.

A CHAT WE SEE A LOT

He took the phone back.

“Now every time I message, they call me slowkar.”

Wah. Battery spoiled, nickname also kena changed.

We looked at the pack. Nice box. Neat PVC heat-shrink. Outside, very professional.

Then we followed the nickel inside.

A 20S 40A BMS, but between series groups 10 and 11, only one wimpy 1P nickel strip carrying the load.

He wanted us to explain why his friends were laughing.

We wanted to know who expected that little strip to do so much work.

Outside quite handsome

His pack wasn’t our first one. Last week another of the same Alibaba packs came in, dead the same way. Two packs, one story.

From outside, no complaints. Nice box. Neat PVC heat-shrink. The label says 72V 20A. Put it on the table and it looks very professional. He paid $400.

“What you expect for $400? Everything nice nice inside also?”

We had a feeling. So we cut the heat-shrink.

Open already, Maggi mee

First thing under the heat-shrink: barley paper, the insulating paper laid over cells and strips. Layers and layers of it. So much that you start to wonder.

“Why so much barley paper? Open and see.”

Under the paper, the red balance wires, the thin leads the BMS uses to read each group of cells. Running across the pack like Maggi mee. Never plan, just do only.

The cells? No brand anywhere. What cell is this? Don’t know. Not the label, not the box.

And all that paper does one more job: once the pack is closed, nobody sees the connections underneath. Those are the ones your throttle depends on.

Group ten meet group eleven

A 72V pack is 20 groups of cells joined one after another. Those are the series groups. Every joint between two groups carries all the current the bike pulls. Every single one.

Between group 10 and group 11, that joint is one nickel strip, about one cell wide. In the trade we call that 1P: a strip sized for a single cell, here carrying the current for the whole pack.

Now the BMS: 20S, 40A. Forty amps is what the board will let through.

“You sure boh, 40A? Through this?”

Remember the confident twist at the starting line? That’s the moment the bike asks for current, and every amp of it squeezes through that one strip. Pull 40A through something that skinny and it gets very, very hot. In our opinion, that’s why both packs died. Not the bike. Not the rider. This little strip.

Bike nothing wrong, he said. Correct. The bike was fine. It was waiting for a battery that never showed up.

Big cable, small tab

Then the two ends of the pack. At the main negative, on group 1, the thick black discharge lead is soldered onto one small nickel tab. We opened the barley paper at the positive end. Same thing: one small tab.

Thick cable, thin tab. Like a six-lane expressway that ends at a void deck gate. Doesn’t matter how wide the road is, everybody still squeezes through the gate.

So that’s one choke point in the middle and one at each end. The big cable outside just makes it look like there isn’t one.

Before you call yourself fastkar

You shouldn’t have to cut open a new battery to find out what you bought. Before you pay, ask the seller four things:

• What exact cell is inside? Make and model.
• Can I see a photo of the inside, especially where the groups join and where the main leads come out?
• Who built it, and who do I call when it dies?
• Why is it so much cheaper than everyone else?

If all you get back is another photo of the box, that’s your answer.

If something isn’t right

Pack swollen, leaking, getting hot on its own or smelling strange? Stop using it and stop charging it. Don’t open it or poke it to check. Get advice from the maker or an authorised service provider, and if you want our view, send us clear photos first. Use only the charger meant for that pack.

Hissing, smoking or heating up by itself is a different situation. Read Battery fire? You got about one minute.

Fastkar Racing: official post-race statement

Sources (2)

• Our workshop inspection of the opened pack.
• Singapore Consumer Product Safety Office: Lithium-ion battery safety tips