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Comment by aeharding | Hacker News Reader

> From what I can tell they use a cargo trailer for gear as well as extra batteries.

This is the main reason if you might ever buy multiple ebikes in your household, buy a drivetrain brand that has generic, swappable batteries that can work on all your ebikes. Buying batteries is expensive (~$1,000 for Bosch).

For example, some ebikes don't have swappable batteries (either they're integrated or are a no-name brand).

The Bosch Powerpack, on the other hand, is ubiquitous and swappable. If I'm going on a long trip, I steal the battery from my other ebike and bring it along (I have a Surly Big Easy cargo bike and a Trek Verve+ 2. My SO also has a Verve+ 2).

Another benefit on buying ebikes with the same powertrain manufacturer is the battery lock can be keyed alike. It simplifies a lot.

(Oh, one last thing! If you go with Bosch, you can get the battery locks keyed alike to Abus U locks.)

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If you can charge your batteries up to 60% when you store them for a longer time rather than 100%, then charge to 100% just before you need them. That will keep them around that much longer. Better still if you can avoid discharging them below 15% soc.

Makes sense for seasonal and recreational riders. We both ride year round though almost daily for transportation.

As for discharging below 15%, Bosch's firmware is pretty smart about this. It keeps a reserve that's used for powering lights for a few hours after the assist cuts off.

Yes, that's at 5% state-of-charge, which is a bit low. If you charge up to 100% and discharge to that cut-off point you will get 300 to 400 cycles out of your battery. If you go from 80% state-of-charge down to 20% then you can get thousands of cycles out of your batteries. That's one of the reasons I designed that pack as large as it is: to stay within the 80-to-20 range on a 100 km trip.

Interesting! I've only gotten that low a handful of times. Definitely a bigger battery would be good if you're going that low on a regular basis.

The “charge to 80%” advice isnt generally useful to PEV riders in 2021

It is true that a lithium _cell_ lasts longer when charged to 80%, but a _battery of cells_ must be “balanced” and PEV BMSes only do that balancing in the constant voltage stage of charging in the hours after the charger indicates the battery has been fully recharged.

For anyone just learning about this, an unbalanced cell is usually the cause of a battery going “dead” and can even be the cause of a fire. Very few batteries die because they have outlived their charge cycle count.

This is different than your cell phone which has at most two cells (but usually one) in the battery. In that case, the BMS can monitor and charge individual cells. In a PEV the BMS usually monitors several groups of cells, and can not charge individual cells.

This can change in the future! I believe electric car BMSes generally do it. But its an added expense and PEV manufacturers have not started spending the money. Ill be happy if another commenter can correct me and show that there is some manufacturer who is ahead of the curve.

By charging and balancing individual cells, you mean group of cells that are connected in parallel (the 4P in 12S4P)? I don't see how or why would you balance individual parallel connected cells, unless you had a different battery configuration.

Simplest "balancers" drain cells that have too high a voltage as you are approaching full charge. You do need to occasionally top the battery off, to keep it balanced. Seeing they already have sense wires and discharge resistors, they could fully monitor state and balance even without top off, but that's additional code complexity.

There are nice BMSs that can shuffle charge between cell groups - they increase range by helping the weakest link, and should help longevity, by again, decreasing strain on the already worst cells. I don't know how common they are, just that they are not typical. There you can also have good and sub-optimal algorithms.

I have heard of individual cell monitoring and maybe balancing, but I have no idea what, how or why it does it.

The pack I built has a balancer, that's what all the red wires on the photograph are for. It uses a charge pump to move some charge around so that the high cells get clipped and the low ones brought up. It keeps the pack within 2 mV. The unit it monitors is the cell group, all 10 of them have a wire to the balancer and a ground for reference. It is very accurate and it wills substantially contribute to the life-span of the pack.

There is an active balancer in the pack I built. It keeps the whole pack within 2 mV.

Oof, $1500 per kWh.

I keep hearing about lithium ion batteries getting so cheap per kWh; when is that going to make it into reasonable-quality products?

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