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I am considering to purchase a bicycle that includes an electric assist with a Shimano E6100 engine. I have not owned any bicycles with electric assist before, and I'm worried about serviceability. In my opinion, a good bicycle should last 20-30 years or longer with regular maintenance.

Pedelecs are more complicated than fully human-powered bicycles. There is more that can break. For most bicycle components, I have quite some freedom in replacing the parts. Hubs, rims, crank, bottom bracket, handlebar, etc., it's rarely a major problem to find something that fits. There may be some exceptions with specialised hub gears such as Rohloff, but with Rohloff I've been lucky so far (they're still in business and their hubs haven't changed much, so finding shifter cables for a 12 year old unit is no problem).

How is it for the components that make a bicycle a pedelec? For engine, battery, cables, plugs, display/computer — do I depend on the original manufacturer (such as Shimano) still producing compatible parts 5, 10, 15 years down the road, or are those components sufficiently standardised such that (provided there is a market for it) I can hope to find third party components that will be compatible?

It would suck to have to replace the whole electric drivetrain system just because the display/computer is kaputt.

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The two E bikes I had from different manufacturers now both made about 5500 km each. During this time, I had to do lots of ordinary bicycle maintenance and repairs, including chain, cassette, brake pad, tire and even freewheel and derailleur replacements. Managed to get it done one or another way so ja, serviceable: electrical part does not stand on the way.

The batteries look somewhat tired but still can do more than half of they initial range, and replacements would be available at the market. The motor hubs and controllers do not show any sign of wear.

Hence you can expect the most wear and maintenance on the non electric part that is the same as for an ordinary MTB.

E-bike seems wearing down faster. I think this is because of the added power of the motor (faster speed for brakes, stronger acceleration, not avoiding hills) and also in my case it sees much more usage, also in difficult weather, winter including.

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  • 5500 km in how much time? No surprise that the non-electric components wear out faster, but I've never had problems servicing those on my now 14-year old Koga touring bike.
    – gerrit
    Commented Jul 9, 2023 at 20:04
  • About two years. They are used for commuting, so kilometers go up pretty fast. One have seen a notable hill on the way, and daily, so brakes got worn earlier.
    – nightrider
    Commented Jul 9, 2023 at 20:25
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Unfortunately, standardization is extremely poor. Because only mid-drives can provide good controllability (since practically no hub drive has a torque sensor), you want to choose mid-drive if you actually expect to be able to enjoy riding the e-bike.

Batteries can be re-celled, but sometimes the manufacturer makes it extremely hard. For example, generally the batteries can't be opened with standard tools. Also some manufacturers like Bosch make the entire battery depend on the continuous availability of voltage. If the voltage is lost, the battery is bricked. This means re-celling needs a continuous power supply, and if that is accidentally disconnected during the re-celling operation, the battery is bricked. Finding someone with experience to re-cell e-bike batteries may be tricky, and you can expect to pay a lot given how hard it has been made. Thus, for e-bikes where replacement batteries are available you probably want to buy a replacement battery. But once those will no longer be available, you want to re-cell. If you have an aging battery and you know you may need to purchase a replacement in the future, consider the likelihood of manufacturer discontinuing support, the easiness and cost of finding an experienced re-celler, and the cost of a replacement battery: it may be best to buy a replacement while you can.

Battery longevity is reduced by continuously charging it to full immediately after every ride. I have a 3-year old Bosch e-bike which I have charged to full after every single ride. Its 13.4 Ah 36 V battery took 126-127 minutes to charge from completely empty (or actually 3% full since there is a slight reserve for running the lights for two hours) to 80% full with a 4 ampere charger. If we can trust the charger to be actually 4 amperes, this might indicate that 8.43 amp-hours went in whereas with a new battery 10.32 amp-hours would have went in. Thus, the battery has about 82% of its capacity left (unfortunately I didn't do the very same test when the battery was new so take the 82% figure with a grain of salt). Of course this is a completely unscientific measurement since a nominally 4 ampere charger may actually be just tiny bit faster. For example my electric scooter has dual 2 A chargers that to me seem more like 2.1 A chargers based on state-of-charge increase rate because the battery charges bit faster than expected.

Unfortunately, e-bike manufacturers make it very hard to charge to 80% full every time. This would increase battery longevity manyfold. You can do it yourself by a timed charge. Generally reasonable rate charges charge at full rate to about 80% full and after that the charge rate begins to decrease, so calculations are easy.

If the e-bike has a percentage battery state of charge indicator with 1% accuracy (like my e-scooter has), do this:

  • I rode my e-scooter to nearby grocery store and had 75% charge left, thus I want 5% more charge
  • The battery is 15 amp-hour, thus I want 15 Ah * 0.05 = 0.75 Ah more charge
  • The dual charges are nominally 4 A together but I suspect them to give approximately 4.2 A, so I want 0.75/4.2 * 60 = 10.7 minutes more charge, let's say 10 minutes for simplicity
  • I attach the charger(s) to a mechanical timer and set it to 10 minutes. The timer will cut electricity automatically after 10 minutes. My timer cost 8 euros; I bought several of them.

If your e-bike only has 0/5, 1/5, 2/5, 3/5, 4/5, 5/5 bar indicator, you should operate it in this manner for most rides:

  • Flat battery (0/5): you know you need 80% charge so calculate timer based on that state of charge
  • Anywhere between 0-20% (1/5): assume 20% and you therefore need 60%
  • Anywhere between 20-40% (2/5): assume 40% and you therefore need 40%
  • Anywhere between 40-60% (3/5): assume 60% and you therefore need 20%
  • Anywhere between 60-80% (4/5): it may already be at 80% so don't charge
  • Anywhere between 80-100% (5/5): definitely don't charge

If you expect to do one occasional long ride, charge it to full immediately before that ride. The shorter the time a lithium ion battery spends at full charge, the better the longevity. Do this only for long rides because the fewer times you charge to full, the better the longevity.

Note this charging plan may leave the battery to 60% state of charge at worst since you may not see the battery state of charge to a high accuracy, some displays only have 0/5, 1/5, 2/5, 3/5, 4/5, 5/5 (5 bars). If this is a problem, consider buying an e-bike with 1% accuracy state of charge meter, or an e-bike with big enough battery.

Enough for the battery. Then what else could break? Lights generally are standardized, lots of compatible ones are available for sale. Cranks may use a rare form of attachment, but you may find compatible cranks for sale. If the attachment is rare, I'd recommend buying several cranks as spare parts while you can buy them. Some e-bikes with dual chainrings may have a rare spider, if you find a compatible spider for sale definitely buy one as spare.

Bottom bracket bearings are integral to the drive unit. Sometimes they may be replaceable by taking apart the drive unit, but that may not be easy. You may be at the mercy of the manufacturer.

Displays are non-standard, expect to not be able to buy a compatible display 20-30 years from now. Mid-drive units have a non-standard attachment to frame, if a drive unit breaks generally you have to expect to replace the entire bike, except if the drive unit breaks between 0-5 years, you may find a compatible one for sale. Rear wheel speed sensor is non-standard so you may want to buy one as spare as long as they are available for sale. Rear wheel magnets may be more powerful than cyclocomputer magnets but cheap to buy so buy as many magnets as you plan to have rear wheels plus maybe 2 extra in case you lose some of the magnets.

Generally, a mid-drive e-bike isn't a tool you can expect to last 20-30 years. I ride an e-bike because it saves me at least 50 hours per year and I expect it to last maybe 10 years with one replacement battery bought in that time. This makes the cost of the bike 4700 euros (cost of bike + 1 extra battery) during those 10 years, but the bike saves 500 hours during those 10 years. A normal comparable bike would have cost maybe 2000 euros and be usable for 30 years so that's about 670 euros during 10 years and the rest during the rest of the 30-year period. So about 4000 euros spent, about 500 hours saved, I'd say a pretty good deal for someone who earns higher-than-average salary.

If your goal is absolutely minimal costs and absolutely maximal serviceability, you may want to look at hub-drive bikes sourced from the communists. They not only cost less but may actually be even more serviceable. Unfortunately, you don't enjoy them as much since those hub-drive units generally lack torque sensor and this absolutely kills the enjoyment. If the goal is to enjoy, pick a good mid-drive unit. If the goal is to go from place A to place B at very minimal cost, then those hub-drive communist bikes may be better, but then again for cost-minimizing choosing a non-electric bike would be even better.

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  • if a drive unit breaks generally you have to expect to replace the entire bike — hm, but if it's possible to convert a human powered bike to a pedal-assist electric bike, shouldn't it also be possible to replace the drive unit without replacing the entire bike? Otherwise it'd actually more attractive to buy a non-electric bike + retrofit, because at least the retrofit can be removed and replaced 10 years later while keeping the rest of the bike.
    – gerrit
    Commented Jul 9, 2023 at 12:06
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    How is it impossible? Isn't this Bafang unit a mid-drive motor retrofit?
    – gerrit
    Commented Jul 9, 2023 at 12:10
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    My aim isn't to be faster. I'm riding a tandem with a person with weak legs, and I find that transporting myself + her + possibly cargo in hilly terrain is exhausting, as even with a very small gear I need to pedal at the best of my ability to make it up even a 6% slope (and I can forget about getting up a ≥12% slope). Having a little electric assist would make for a more enjoyable ride with less exhaustion and less pushing.
    – gerrit
    Commented Jul 9, 2023 at 12:22
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    Battery management systems are capable of managing charge, e.g. by charging to 80% when the battery is new, and making more of the full capacity available for charging as the battery ages. Do we know that these types of BMS are uncommon on ebikes? For current generation systems by mainstream companies, I have to imagine they would be pretty common. In my experience, micromanaging your battery's charge is impractical for the average consumer. You should do it if you are this way inclined, but your average rider is going to think this is absurd.
    – Weiwen Ng
    Commented Jul 9, 2023 at 13:08
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    "you want to choose mid-drive if you actually expect to be able to enjoy riding the e-bike" This is just wrong.
    – kmm
    Commented Jul 10, 2023 at 0:11

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