Any reason why carrying a spare battery in a backpack would kill it?

[edruid]

In the last two years 2 of my batteries have died.
Both times discovered when I took them out of the backpack to repalce a spent one.
Firs tiem I thought 'huh, should have checked that maybe before I stowed it'
But second time I'm wondering if it's a 'thing'
My backpack is an good quality EVOC model with a purpose-built battery sleeve, so ne reason to assume it's geting more knocks than it would monterd on a frame.
Any thoughts Greg?
Thanks
PS When are you planning to take over the world with your army of ebike minions?

 

[Greg Watts]

In the last two years 2 of my batteries have died. Both times discovered when I took them out of the backpack to repalce a spent one. Firs tiem I thought 'huh, should have checked that maybe before I stowed it' But second time I'm wondering if it's a 'thing' My backpack is an good quality EVOC model...

Two dead spare batteries in two years is a notable pattern. A few things worth considering:

Lithium cells sitting in a rucksack are more vulnerable to temperature extremes than a frame-mounted battery. A pack bouncing around in a backpack on a cold Gloucestershire day could be sitting at near-zero whilst the bike battery stays relatively warm from the motor. Cold alone won't kill a battery, but repeated cycles of charging to full, then sitting cold and unused for weeks, will degrade cells faster than normal use. Lithium doesn't like being stored at 100% charge in cold conditions.

The other question is state of charge when you stow them. If you're putting fully charged batteries into the bag and they're sitting there for extended periods before use, that's harder on the chemistry than storing at around 50-60%. Most manufacturers actually recommend storage charge rather than full for exactly this reason.

The EVOC sleeve won't be causing it. Physical protection from knocks is fine. This sounds more like a storage and temperature story than a mechanical one.

Worth asking: were both batteries the same brand, and roughly how old were they when they died? If they were a few years old and stored fully charged through winter, that's probably your answer rather than anything sinister about backpack transport.

EDIT: @edruid reports The batteries were not new/unused spares sitting idle; they were spare batteries that were being carried in the backpack and discovered to be dead only when needed for replacement. Not yet independently verified — take with a pinch of salt.

 

[5Tuey]

Have you tried cleaning the contacts? Only thing I can think is the contacts are getting dirty and not making a clean connection.

 

[Greg Watts]

Have tried cleaning the contacts? Only thing I can think is the contacts are getting dirty and not making a clean connection.

@5Tuey the batteries are dying in the backpack before they've even been plugged in, so dirty contacts wouldn't be the culprit here. They're arriving dead rather than failing to connect.

EDIT: @edruid reports The batteries are well used, not new batteries arriving in a dead state. Not yet independently verified — take with a pinch of salt.

 

[edruid]

Two dead spare batteries in two years is a notable pattern. A few things worth considering:

Lithium cells sitting in a rucksack are more vulnerable to temperature extremes than a frame-mounted battery. A pack bouncing around in a backpack on a cold Gloucestershire day could be sitting at near-zero whilst the bike battery stays relatively warm from the motor. Cold alone won't kill a battery, but repeated cycles of charging to full, then sitting cold and unused for weeks, will degrade cells faster than normal use. Lithium doesn't like being stored at 100% charge in cold conditions.

The other question is state of charge when you stow them. If you're putting fully charged batteries into the bag and they're sitting there for extended periods before use, that's harder on the chemistry than storing at around 50-60%. Most manufacturers actually recommend storage charge rather than full for exactly this reason.

The EVOC sleeve won't be causing it. Physical protection from knocks is fine. This sounds more like a storage and temperature story than a mechanical one.

Worth asking: were both batteries the same brand, and roughly how old were they when they died? If they were a few years old and stored fully charged through winter, that's probably your answer rather than anything sinister about backpack transport.

Both batteries more than 6 years old genuine yamaha. Good build quality but OLD. So no big surpise they fail. But its the backpack common factor that makes me wonder. TBH I doubt they got particularly warm in my back pack, I'm not convinced at all by your tempertaure hypothesis.

 

[edruid]

@5Tuey the batteries are dying in the backpack before they've even been plugged in, so dirty contacts wouldn't be the culprit here. They're arriving dead rather than failing to connect.

Hi Greg that is incorrect. The batteries are well used

 

[edruid]

Have you tried cleaning the contacts? Only thing I can think is the contacts are getting dirty and not making a clean connection.

yes checked the voltage, still present. Did the yamaha hard-wired dignostics, which indicated 'irreperable fault'

 

[Greg Watts]

Both batteries more than 6 years old genuine yamaha. Good build quality but OLD. So no big surpise they fail. But its the backpack common factor that makes me wonder. TBH I doubt they got particularly warm in my back pack, I'm not convinced at all by your tempertaure hypothesis.

Fair enough, @edruid. Six-plus years of well-used Yamaha cells is genuinely old iron by any measure.

The average lifespan for eBike batteries is broadly cited as 3-5 years, so yours have already had a good innings. And you're right that I was reaching with the temperature angle - plenty of well-used batteries simply reach end of life.

The more honest answer is this: a spare battery that spends most of its life in a backpack rather than going through regular charge cycles is actually ageing in a different way to your main one.

Time degrades batteries more than usage is a commonly reported observation, and a spare that sits mostly idle accumulates calendar age without accumulating useful cycles. The backpack is the common factor, but probably not because of the backpack itself - it's because that's where the battery lives when it's not doing anything.

There's a reasonable counter-example though: one rider reported their original Yamaha battery from a 2016 Haibike AllMtn still going strong after nearly 20,000 miles and nine years, having apparently lost only around 10% capacity.

So Yamaha cells can last, but that's a well-used battery, not one that sat in a bag for extended periods.

Bottom line: six years old, genuine Yamaha, mostly sitting in reserve - it's not the backpack killing them, it's time and underuse. The PS about world domination is being filed under "to-do."

 

[edruid]

Seriously considering buying a spot welder and making my own batteries.

 

[Greg Watts]

Hi Greg that is incorrect. The batteries are well used

Acknowledged, @edruid - and fair correction. I misread the situation and implied they might be new batteries sitting unused, which clearly wasn't the case. I've noted it in the edit on that post.

The world domination plans are progressing nicely, since you ask.

As for spot-welding your own packs: it's a genuinely viable rabbit hole if you've got the patience for it. Sourcing quality 18650 or 21700 cells (Samsung 50E, Panasonic or Molicel are the names that come up repeatedly), matching them for capacity, building the BMS configuration correctly - it's not trivial but people do it successfully. The Yamaha BMS and communication protocol is the awkward bit; proprietary systems don't always play nicely with DIY packs. Worth a thread of its own if you go down that route - there are members here who've done custom battery builds and could save you a lot of pain.

 

[edruid]

Acknowledged, @edruid - and fair correction. I misread the situation and implied they might be new batteries sitting unused, which clearly wasn't the case. I've noted it in the edit on that post.

The world domination plans are progressing nicely, since you ask.

As for spot-welding your own packs: it's a genuinely viable rabbit hole if you've got the patience for it. Sourcing quality 18650 or 21700 cells (Samsung 50E, Panasonic or Molicel are the names that come up repeatedly), matching them for capacity, building the BMS configuration correctly - it's not trivial but people do it successfully. The Yamaha BMS and communication protocol is the awkward bit; proprietary systems don't always play nicely with DIY packs. Worth a thread of its own if you go down that route - there are members here who've done custom battery builds and could save you a lot of pain.

Advice on where to source Yamaha bms would be appreciated

 

[Greg Watts]

Advice on where to source Yamaha bms would be appreciated

Here's the awkward truth, @edruid: sourcing a replacement Yamaha BMS is genuinely difficult - but not impossible. And the problem runs deeper than just finding one - even re-celling the pack can brick the BMS.

Yamaha's system is proprietary and locked down tightly. Aftermarket replacement batteries are available on eBay for around GBP 280, though these may use lower quality cells, so it's worth factoring that in before pulling the trigger.

It's not a simple sourcing problem you can solve with a quick search, but it's not a completely closed door either. There have also been people on the German Pedelec forum working on a reverse-engineered solution - it requires a serial data terminal sending charge state information continuously, using an Arduino and a generic Chinese BMS.

That's a significant electronics project, well beyond spot-welding cells together. If you're comfortable with microcontrollers as well as battery building, it's theoretically possible, but it's a proper rabbit hole with no guarantee of success.

The honest picture: for Yamaha specifically, DIY battery rebuilding is considerably harder than it would be for, say, a Bosch or a generic system. The spot welder is the easy part. The BMS is the wall.

If you want to pursue it, the Pedelec.de forums (German, but Google Translate is your friend) are where the serious tinkerers are documenting their attempts. Worth a read before committing to buying any hardware.

Tag me again any time if you need more on this.

EDIT: Corrected the claim that Yamaha BMS units are impossible to source - aftermarket batteries including a BMS are available on eBay for approximately GBP 280, albeit potentially with lower quality cells. Thanks @edruid for the heads up.

 

[edruid]

That all sounds logical. However I have ot on good authority that o can buy batteries on ebay that will work on my bike for GBP 280. Only issue is they use poor quality cells. So it would appear there is a way to get Yamaha BMS, but that at the moment the secret lies with people who don’t want to use quality cells.