A Deeper Dive into Running Out of Charge on Bosch Batteries

We’ve touched on battery topics a few times like special considerations for cold weather, and how to extend your range with dual battery setups. More best practices for Bosch battery care can be found in the updated Battery Guide 2021.

A question we’ve gotten a lot lately though, is:

What actually happens when you run out of battery while riding your e-bike?

First, when you hit “no bars” on your battery indicator, the system will remain on but the assistance mode will switch off. The bike offers no pedal assistance to you even though the system is still on.

Why? The battery holds reserve power to run the lights for at least two hours. The amount of power held on reserve this way is dependent on the power required for the lights. If your system is configured for brighter lights, the system knows to save more power to keep them powered. If you have a Kiox or Nyon display, you might have noticed that this is around 2 or 3% on the battery indicator.

If your bicycle additionally has integrated e-shift, it also holds reserve power to power through at least 50 more shifts.

Then, If you keep riding the battery all the way down to 0% on the indicator, the entire bike will shut off. If this happens, it is important to reconnect your battery to a charger as soon as you have completed your ride and get it at least partially charged. Otherwise, your battery can reach what is called “deep discharge” where it will no longer take a charge and must be replaced. Lithium ion batteries, unlike lead acid batteries found in cars, cannot be “jumped” or re-awaken from this state. According to Bosch, fully discharging a battery into deep discharge is considered misuse and is not covered under warranty. 

How does this deep discharge scenario actually happen? 

The answer is complicated, and to be honest, I do not fully understand. Battery experts, drop me a line, I would love to hear! My understanding is basically that the battery is holding a teeny bit of charge left even when it is telling you it has no more power to give. That amount of charge is required for its internal processes, including the Battery Management System. Batteries very slowly lose charge over time even without use (commonly referred to as “trickle discharge”), so if you run your battery all the way down to its last teeny reserve, it will then trickle discharge that power, and there will be nothing left and become unusable. I reached out to Bosch and they summarised it,

“All modern lithium ion battery cells, whether they’re in a Bosch PowerPack or some other device, contain a protection circuit that, for safety reasons, renders the cell unusable if over-discharged.”

I also asked Bosch about exactly how bad for the battery it is to run it down to system power-down, 

“I would definitely avoid doing this if possible. It’s not the worst thing for the battery, but it’s not great either. I recommend not making a habit of it, but also not worrying too much if it happens on occasion”

I would agree with trying to avoid running the battery down to system power-down if possible, but the important thing is to charge the battery as soon as possible after doing so. If you are regularly running out of battery on your route, consider checking out if there is a way to set your bicycle up for dual battery.

How fast does it trickle discharge?

The battery will lose charge slowly over time, but how slowly though? This is an important consideration for fair-weather riders who might be putting their bike away for nine months of the year. 

According to Bosch, high-quality Lithium ion batteries lose charge at approximately 0.5%/month. This means if your battery had only 4% charge when you put it away, it would be into deep discharge by the time summer rolled around next year. Lithium ion batteries are also sensitive to temperature, so storage below 32 F (0 C) or above 86 F (30 C) can increase the rate of trickle discharge. This scenario should be avoided by bringing your battery up to a medium charge level before putting in storage. 

So how should I store my batteries?

Bosch batteries (or any high quality Lithium ion e-bike batteries) should ideally be stored between 32 and 68 degrees F (0-20 C) and between 30 and 60% charge level. Avoid leaving the battery plugged in for a long time, and avoid leaving it for long storage at full charge. 

So when winter comes and you’re putting your bike away for the season, charge the batteries up to 60%, put the bike somewhere at room temperature, and let it sit. If the bike lives somewhere that might be the outside temperature like a shed or uninsulated garage, consider removing your batteries and bringing them in the house for secure room-temperature storage during the winter.

If the whole summer passes by without a ride, while you theoretically have many years before it trickles out of the ideal range, we still recommend taking a moment to check the charge level again before starting another year of storage.

Bosch makes a special Battery Capacity Tester tool, that among other things, can be used to set the charge level to 60% when putting the battery into storage. Bosch recommends doing this if planning to leave the battery unused for three or more months. We are thrilled to say we now have one of these cool tools! Give us a call and we can arrange to do this for your batteries in advance of your planned storage. 

What if my battery suddenly won’t respond?

Another consequence of trickle discharge and deep discharge being considered user fault is that if you are having a warranty issue on your battery that it suddenly becomes wholly unresponsive, the battery will continue to trickle discharge. This is especially a concern if it was at low charge before it finally died all the way.  If the battery trickles all the way into deep discharge, we won’t be able to determine that it was a warranty. 

So if your battery has suddenly become unresponsive, especially within the two year warranty timeline after purchase, please reach out to us right away so we can see if it can be revived, or if we can pull the error codes to make the warranty claim smoother. 

What is the normal lifespan of the battery?

In a battery that does not experience a warranty shut-down or deep discharge, what life span can you expect from it? There is no single answer as it depends on use and storage conditions. Like our cell phone, as the battery ages, its capacity decreases over time, meaning we get less power per charge. Bosch cites that after 500 charge cycles (over 10,000 miles), the user can still expect the battery to have 60-70% of the original capacity.

The basic diagnostic report we run during tune-ups will show how many charge cycles your battery has been through. But the Battery Capacity Testing tool can also be used to assess the current capacity of your battery – you can request this extra diagnostic as well when your bike is in for service. It takes several hours to run so this is a service that must be done by appointment. 

When your battery has reached its end of life, whether by unresponsiveness or the capacity having decreased to unusably low, we are an e-bike battery recycling collective site. Bosch batteries cannot be refurbished, but we can get them properly disposed of for you. More on that coming in a future post.

Any further questions? drop us a line to service@familycyclery.com