Li-ion Cycle Life and BMS questions

Hey goTenna hardware team or @anon62894636!

I have a few questions regarding the li-ion/li-po pack inside the goTenna mesh, what’s the rated cycle life of the battery and have you guys though about introducing a “connected external battery mode/always powered mode” with a modified charging profile (reduced max voltage charge to, say 4.05V, and reduced auto recharge voltage to around 3.5V ) to extend battery cycle longevity?

I’ve worked with li-ion batteries for a while now and most of the industry agrees that a lower max charge voltage (not fully charged) paired with a shallower depth of discharge (not fully discharged) increases the usable life of a battery by multiple times. This could mean going from a 1 year constant use cycle to 3 years.

Since this mode would primarily be used for stationary relays which seem to often be paired with external battery packs and solar cells the proposed reduced max storage of the internal gotenna mesh battery due to the changes I listed above is not really a big problem, however it would mean much lower maintenance costs (or complete unit replacement costs) to triple the lifespan of a unit for power users who have goTenna mesh units constantly on every day as relay points with or without external packs.

Here’s a quick source on the topic:

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I would very much want the next “hardware” model to have a replaceable battery. I just spent 20 min ripping open one of my goTenna Mesh units for a project and I don’t see a way to easily replace the battery. Not being able to replace the battery is going to be a problem in the future. I know a lot of companies are going this way but its starting to become a problem as in Apple’s “battery issue” where they had a bad batch of batteries and are now replacing them.

The battery is rated to contain at least 80% capacity after 500 cycles of full charge and discharge. It’s an interesting idea! We’ve certainly considered the options here and it would take a hardware update. I think having an auto-reboot would more or less resolve this issue. We’ve discussed that in-depth: How to make a unit stay on?!

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A few photos of the beginning of my extended (external) battery pack project.

I plan to connect this up to a solar cell (at this point I do not plan to use the Voltaic V15 battery back)

Is the BMS on the battery or on the goTenna board?

The battery is rated to contain at least 80% capacity after 500 cycles of full charge and discharge. The power is drawn accordingly.

Sorry I meant the “Battery management system” and charging circuit. I’m assuming they are part of the goTenna PCB board and not integrated into the battery.

Yes, that is correct, the charging circuit is on the PCB.

If you’d like to replace the battery, you should replace it with a Standard Single Cell Lithium Ion Polymer (LiPo) battery. 3.7V typical, 4.2V Max.

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Hi @anon62894636, thanks for the response! I believe the linked thread is referring to an auto boot after the battery dies and is recharged. The change I’m suggesting has to do with modifying the charge profile to increase cycle life and reduce the time the battery stays near 100% and near empty. We’ve seen this behavior in the past with a lot of laptops that are constantly plugged into power adapters and stay at 100% charge for extended periods of time, this usually leads to premature battery degradation. It’s also the reason why most modern li-ion based EVs (Tesla in particular) recommend that users normally never charge to full (range mode) and recommend charging to around 80% or so to prevent capacity loss over time.

Some more sources regarding this subject.

The Jeff Dahn video is a long but extremely informative piece from one of the forefront experts in the field.

Examples of manufacturers utilizing custom max charge rates to increase cycle life:



The Lenovo example is the exact implementation that would be useful, granted the end user doesn’t need to be able to adjust it that finely, rather goTenna can have a set profile for “always connected” mode rather than constantly charging the battery to 100% after it drops a little bit.

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I second a replaceable battery, as well as configurable options for relay mode battery management (100%, 80%, and 50% charge levels).

What kills lithium ion batteries the fastest is staying at or above 4.2 volts. Laptops and cell phones love to overcharge their batteries (I’ve seen 4.4 volts in a Droid Turbo and XPS 13). 4.2 volts should be the highest a battery is taken.

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