The 5-second answer
An e-bike isn't something that just sits there and doesn't wear out when you don't ride it. Lithium-ion batteries slowly lose charge on their own even in storage, so if you leave one nearly empty for a long time, the voltage keeps sinking and the battery ages faster.[1][2] As of 2026, genuine replacement batteries run from about 49,000 to 68,000 yen in the examples I found, which can look like 30 to 50% of the price of a new bike.[3][4][5][6][7] And yet average battery pack prices worldwide fell 8% in 2025, and lithium prices in early 2026 were still about 70% below the 2022 peak.[8] So "lithium is expensive, so everything is expensive" doesn't explain it. It only makes sense once you look at the economics of keeping spare parts available for old models for years.
1. I Opened the Front Door, and My Bike Vanished for 2,700 Yen
Before moving house, I had to get rid of a broken electric-assist bicycle.
The pricing was simple:
- Pickup visit: 2,000 yen
- Disposal: 700 yen
- Total: 2,700 yen
He handled it right at my front door, and that was that.
Booking a bulky-waste collection, carrying the thing out, figuring out what to do with the battery: all of it disappeared at once. Think of it as outsourcing the triple whammy of "heavy, takes up space, and the battery is dead" for 2,700 yen, and it's a bargain.
Then the bike shop guy who came to pick it up told me something.
"If you just leave it sitting without riding it, the battery drains, goes down close to zero, and that can damage it."
And just like that, a simple disposal turned into a crash course in battery engineering and spare-parts management.
2. "It Breaks If You Don't Ride It" Is Half True. The Real Danger Is Leaving It Near Empty
Yamaha's official FAQ is pretty clear. If you store a battery empty, it keeps self-discharging down to an even lower voltage, and that speeds up its deterioration.[1]
For long-term storage, it says to take the battery off the bike, keep it indoors somewhere dry and at a moderate temperature, and leave about one or two of the charge indicator lights lit. It also says to check the charge once a month and top it up a little once it drops to a single blinking light.[1][2]
So the point isn't simply
you don't ride it → it always breaks.
It's more like
low charge → left alone for a long time → self-discharge → even lower voltage → faster aging.
With a regular bike, "I haven't ridden in six months, time to pump up the tires" can be the whole story. With an e-bike, you get a "home appliance maintenance event" mixed in.
You're not even riding it, yet it needs maintenance. And it's exactly when you're not riding that you tend to forget.
E-bike: "You haven't been riding me lately, have you?"
You: "Yeah."
E-bike: "Then I'm adding a battery management task for you."
You: "But I'm not even riding you?"
3. And a Replacement Battery Is 50,000 Yen. That's Huge Compared to the Bike
Looking at official manufacturer information as of August 2026, a replacement 15.8Ah battery for the Yamaha PAS (a popular electric-assist bicycle line in Japan) costs 49,940 yen.[3]
For Panasonic, one example is a 25.2V, 16Ah battery from the current lineup at 49,000 yen.[4] On the older-standard side, there's a 13.2Ah at 59,700 yen and a 17.6Ah at 68,000 yen, and these were repriced on June 1, 2026.[5]
Now look at new bikes.
The Panasonic ViVi SX is 122,000 yen and the ViVi DX is 143,000 yen.[6] The Yamaha PAS Ami is 158,000 yen, and that price includes the battery and a dedicated charger.[7]
That gives you:
- 49,000 yen ÷ 122,000 yen ≒ 40%
- 59,700 yen ÷ 122,000 yen ≒ 49%
- 49,940 yen ÷ 158,000 yen ≒ 32%
So what we said in conversation,
"The battery costs about half as much as the bike itself. Isn't that too expensive?"
wasn't a sloppy exaggeration. Depending on the combination, it's almost exactly the math.
4. But Lithium Has Gotten Cheaper. So Why Don't Replacement Batteries Come Down?
This is the most interesting part.
According to the IEA (the International Energy Agency), average battery pack prices worldwide fell 8% in 2025. Lithium prices in early 2026 were higher than a year earlier, but still about 70% below the 2022 peak.[8]
That means an explanation like
"Lithium is at an all-time high lately, so e-bike batteries cost 50,000 yen"
doesn't hold up well.
That said, the IEA figure is a global average for battery packs, covering EVs, stationary storage and so on. It isn't the retail price of a genuine replacement e-bike battery in Japan, so the two numbers shouldn't be treated as the same thing.
Still, you'd think that if raw materials get cheaper, retail replacement parts should fall in proportion.
But a replacement part carries a lot besides the cells:
- A battery management system (BMS) for charging, discharging and temperature control
- A dedicated case and connectors
- Checking compatibility with the bike
- Quality guarantees and safety measures
- Stock of old standards
- Production and setup costs for small demand
- Shipping and labor
- The cost of supporting old models for a set period
So the price structure is not "X kg of lithium × the market price."
Manufacturers don't publish a cost breakdown saying what each item costs, so the list above is my analysis based on how manufacturing and spare-parts supply work. Still, it's a bigger stretch to assume that cheaper materials mean the suggested retail price of spare parts drops at the same rate.
5. "Spare Parts," Not "Supplied Materials." The More Models You Have, the Worse the Back End Gets
A phrase came up in the middle of the conversation.
"What do you call it when a manufacturer keeps supplying the old stuff? Shikyuhin?" (a Japanese word meaning goods handed over by a client)
The closer term is service parts / repair parts. Panasonic officially uses the term "repair performance parts," and for electric-assist bicycles it sets the retention period at 8 years after production ends. It adds that depending on how easily materials can be sourced, supply may end earlier than that.[5]
"Shikyuhin" is a word used when you're handed materials or parts by a client and use them in your work, so it's something else entirely.
And what makes repair parts so hard is that releasing a new model never reduces your obligation to the old ones to zero.
You release new model A.
The next year, B.
Then C.
On the sales floor, A gets replaced by B, then C, but on the service side, both A and B stay around.
On top of that, you pile up:
- Different capacities
- Different connectors
- Different BMS versions
- Charger compatibility
- Differences between bike generations
- Colors and case shapes
- Substitute parts with revised specs
During mass production, you can crank out the same thing in huge batches. Once it's old-model repair, demand is thin and hard to predict, yet "whoever needs it needs it right now."
It's a lineup of everything a manufacturer hates.
Even if material costs fall, if lot sizes shrink, setup effort grows, part numbers to manage multiply and storage periods stretch, the unit price of the part doesn't simply go down.
The fact that an older, smaller-capacity battery can cost more than a newer, bigger one is an intuitive example of how capacity alone doesn't decide the price.[4][5]
6. A Battery Is Also a Safety Part. "Cheaper Is Always Better" Doesn't Really Work
Japan's Ministry of Economy, Trade and Industry (METI) says 36 accidents involving electric-assist bicycle batteries were reported in 2024.[9]
Of course, you can't draw a simple line from 36 accidents to a particular price for genuine parts.
But lithium-ion batteries pack a lot of energy, and when something goes wrong, there's a risk of overheating and fire. Yamaha also tells customers to use genuine parts for replacement batteries and says non-genuine use isn't covered by the warranty.[3]
In other words, a replacement battery is sold not as
"a box that holds electricity" but as a vehicle part that includes safety management.
You might be able to make it cheaper by cutting corners there, but this isn't a product where the cheapest one wins.
7. For This Kind of Hands-On Job, the Human Guy Is Still Strong
Plenty of bike maintenance steps can be automated. But what gets brought into a neighborhood bike shop isn't like a mass-production line:
- Different model years
- Different brands
- Different kinds of rust
- Different ways it was used
- Different crash histories
- Different noises
- The only symptom description is "something feels off"
If the job is tightening the same part at the same position every second, a machine wins.
But things like
"This one's ten years old, and the battery's dead."
"This wobble is coming from here."
"With that noise, it's probably this."
"Honestly, scrapping it is better than fixing it this time."
That kind of small-batch, many-variety work plus on-the-spot diagnosis plus talking with the customer is still a place where skilled humans are very hard to replace.
AI can help with diagnosis, but it won't show up at your front door and carry off a bike weighing around 25 kg.
For now, the best interface is a middle-aged guy.
8. And This Guy's Sunglasses Are Huge
I've been seriously thinking all this time about:
- Over-discharge
- Self-discharge
- Lithium prices
- The BMS
- Repair performance parts
- The growing number of models
- Inventory management
- Safety
But what actually showed up was
a flashy-looking middle-aged guy in absurdly huge sunglasses at my front door.
Looks: like he runs the BBQ at the beach.
Skills: can explain exactly why an e-assist bike died.
Job: hauling away a heavy bike.
Bill: 2,700 yen.
Personality: a genuinely nice guy.
That's a lot of information.
It started as a simple "got rid of the bike, thank goodness," but after about five minutes of chatting, it led to
"Why does a battery get damaged when you leave it alone?" "Why are genuine replacement batteries still expensive when lithium gets cheaper?" "Why do products with lots of model changes turn spare parts into hell?"
Chatting with local tradespeople sometimes teaches you more about how manufacturing really works than a university lecture.
Wrap-Up: I Threw Away a Bike for 2,700 Yen and Picked Up the Economics of Spare Parts
Here's the whole story in one line:
With an e-bike, "not riding" doesn't mean "preserved." Leave the battery alone and it becomes something you have to manage. And the price of a replacement battery is easier to understand if you see it not just through lithium prices but as a spare-parts business that supports old models for a long time.
The practical lessons are simple:
- If you won't ride for a long time, check the manufacturer's recommended charge level and storage conditions.
- Avoid leaving it empty.
- Before buying a replacement battery, compare the price to the bike's value and weigh repairing, replacing or scrapping.
- The older the model, the more you're paying for "spare-part value," not "capacity value."
- Even with huge sunglasses, a guy who explains things accurately and works fast is a good bike shop.
That last one isn't research.
But it might be the most repeatable finding of all.
FAQ
Q1. Will an e-bike battery always die just because I don't ride?
No. The problem isn't so much not riding for a long time as leaving the battery at a low charge so that self-discharge keeps going. Other things, like high heat, also wear it down. Following the manufacturer's storage conditions is the safe way.[1][2]
Q2. Can I just leave it fully charged?
For long-term storage, Yamaha recommends about one or two indicator lights, and says that leaving it fully charged for a long time speeds up deterioration too, not just leaving it empty.[2]
Q3. Why can an old, smaller-capacity battery cost more than a newer, bigger one?
Because capacity alone doesn't set the price. Small-volume supply of old standards, keeping parts available, compatibility and stock may all play a part. This isn't a claim about any manufacturer's actual cost breakdown, just an analysis based on how spare parts work.[4][5]
Q4. Are "service parts" and "shikyuhin" different things?
Yes. Service and repair parts are parts supplied for repairs and maintenance after a sale. "Shikyuhin" is used when a client hands materials or parts to a supplier to be processed or assembled.
Q5. If a replacement battery is 50,000 yen, should I just buy a new bike?
There's no single answer. Compare the bike's age, the condition of the tires, brakes and drivetrain, how often you'll ride it, and the price of a new one. If you'll hardly ride it, even the storage upkeep after replacing the battery becomes a cost.
Internal Link Ideas
- Why does a lithium-ion battery lose charge even when you're not using it?
- Why are spare parts so expensive? Lots, inventory and model management after production ends
- Repair or replace? Thinking in terms of remaining value and replacement part prices
- Jobs where human mechanics are still strong: small batches, many varieties and hands-on diagnosis
- A checklist for storing an electric-assist bicycle long term
