Android Question Charging

David Riley

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I have a Nexus 7 tablet used on permanent charge. After several years, unsurprisingly, the battery has ballooned, bending and pushing out the display. There is great risk of fire, explosion, and toxins.
To solve this I am reading the battery level (0 - 99) and switching the charger on via bluetooth. For testing it is on below 70 and off above 72.
What do people think would be the best setting ? I was considering on below 40 and off above 60.
 

aeric

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If I understand your question correctly, you are asking what is the minimum percentage of battery to start recharge and maximum percentage to unplug the charger to keep the battery life longer. For me, I don’t care much. I charge when the indicator turn red (below 20%) and switch off the charger when it is 100% full. When the battery capacity drops to lower than 50%, I will consider to replace the battery. Battery normally last 2 years. My last Sony Xperia ZR last for 4 years until it started become fat.
 
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David Riley

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It is time to get a new one. The Nexus probably has an outdated OS and it is not worth burning a home to save 50 bucks.
Thanks. But you have missed the point. This tablet was only a test and has no importance. I am wanting to find the safest and longest surviving way to leave a tablet on permanent charge for the future. I manufacture systems used in transport vehicle cabs.
 
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agraham

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I would think the best setting is a low as possible to minimise the energy stored in the battery but if it was me I would not take the chance and I would try changing the battery. They seem very cheap on eBay and if it is a test device you don't have to put it back together very neatly!
 
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David Riley

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I would think the best setting is a low as possible to minimise the energy stored in the battery but if it was me I would not take the chance and I would try changing the battery. They seem very cheap on eBay and if it is a test device you don't have to put it back together very neatly!
A very good point to have the lowest energy in the battery for safety. I'd not thought of that, and exactly the sort of suggestion I was hoping for.
Again this is about a solution for future safety and extending life. Not about this particular device.
Your post is at a wrong forum, I'm afraid.
I disagree. This is about safety and most users on this forum leave devices on charge and should consider the risks and ways to minimize them. My code is all B4A.
 
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José J. Aguilar

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I think I read some place, if you are going to let a device long time without using, let the battery to 50% or something like that.
Maybe this would be interesting to you:
 
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David Riley

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Sorry, but I don't understand. Your first post seems to refer to a specific device with a specific problem. :confused:
It was a long term test of a new product to test and look for possible problems. The likelyhood of explosion, fire, and toxins is a very real problem in a vehicle cab. I have to find a solution before the new product can be sold. The driver cannot manage the battery charging or watch for signs of imminent failure. The problem applies to all tablets and phones with internal batteries.
 
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David Riley

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I think I read some place, if you are going to let a device long time without using, let the battery to 50% or something like that.
Maybe this would be interesting to you:
Thank you. That says the lower the voltage the better. So maybe 10,20 ? With agrahams low energy too. But why not 10,15, or 5,10 ?
 
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agraham

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I realise that I don't know the full range of considerations you will be taking into account, particularly the quantities involved which will make a big difference to the options open to you. But conveniently ignoring all that here's my take.

What's the expected life of this product/the vehicle it's installed in? If it's more than three years then an off-the-shelf Li-ion powered tablet may not be the ideal device to use.
Perhaps an industrial Android tablet - more expensive but probably a whole lot better built and better sealed. A decent supplier of such things should be able to have a rational discussion with you about your concerns and requirements.

If it is permanently installed in the vehicle something running off the vehicle's electrical system would be optimal. For a limited number of devices perhaps a commercial tablet with the battery stripped out. See industrial tablet supplier above. Most tablets will run when when connected to a charger with no battery present or you simulate charging the missing battery with a 3.7V Zener in series with a resistor (Afterthought : put a supercapacitor across the Zener and if the Zener won't take the forward current if the supply fails put a normal diode in series with the Zener. Experimentation needed :)) . For greater device numbers perhaps a custom device from an industrial supplier, or maybe there is one out there waiting to be discovered.

In the extremis your own engineering solution using bought-in components and displays packed appropriately.
 
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David Riley

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Thank you for your thoughts. You have highlighted the dilemma of low volume manufacturing. Wanting to buy in a mass produced product with oodles of features at bargain price. But having to make and sell something that looks rubbish at an eye watering cost.
The reason for my post was that having succeeded in making a potential solution work, I could not decide on the numbers to enter, or if failure would be completely prevented.
It is perhaps strange that devices do not have the ability to switch off charging under user program control. Perhaps they will soon. If so my question becomes more relevant to many people.
Will just charging the bottom 10% cause other problems and shorten life ? Is it better to charge 15 minutes at a time or just a few seconds on and a few off ?
 
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agraham

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You have highlighted the dilemma of low volume manufacturing.
Been there, done that, for hardware and software all my working life!

I think you may be overthinking this unless your customer has some specific safety requirements. After all the driver is most likely carying his own tablet or even a company phone which would have similar concerns. Why not use a cheap tablet and change them out every year or so?

I don't know the figures nor have I seen a graph of the potential for a dangerous battery condition versus age and charging cycles. If it is truly a concern then the last place to try to get advice is from a forum like this - even from me :). I would do a lot of internet research and maybe find a battery expert to talk to face to face.
 
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AHilton

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Will just charging the bottom 10% cause other problems and shorten life ? Is it better to charge 15 minutes at a time or just a few seconds on and a few off ?

To actually answer your question, yes, charging a battery to less than it's full charge will shorten its' life. Different battery chemistry gives some different results but as a rule, charging it to 100% and keeping it there (+/-) is best for the battery. Depending on the devices' charge circuits, it may not make a difference if you leave it plugged in (the device will not 'overcharge') but that's rare these days in consumer electronics. For those, overcharging is almost as bad as keeping it undercharged. Short cycling the charge is bad. Charge rate is a big consideration, too, but it appears like you're just going to use the devices' own charger anyway so you're stuck with however the mfgr decided to do it (likely the cheapest way).

I won't speak to the safety issue you brought up earlier.
 
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David Riley

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To actually answer your question, yes, charging a battery to less than it's full charge will shorten its' life. Different battery chemistry gives some different results but as a rule, charging it to 100% and keeping it there (+/-) is best for the battery. Depending on the devices' charge circuits, it may not make a difference if you leave it plugged in (the device will not 'overcharge') but that's rare these days in consumer electronics. For those, overcharging is almost as bad as keeping it undercharged. Short cycling the charge is bad. Charge rate is a big consideration, too, but it appears like you're just going to use the devices' own charger anyway so you're stuck with however the mfgr decided to do it (likely the cheapest way).

I won't speak to the safety issue you brought up earlier.
I have respect for opinions that go against the crowd, since it usually means they are considered, rather than just repeated from elsewhere. But I wonder if you are thinking of lead acid batteries ? They certainly should be kept fully charged. I thought Li-ion were also damaged by leaving discharged. But the link above suggests lower charge is better. What leads you to think short cycling is bad ?
 
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David Riley

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It occurs to me my solution may make matters worse. The original problem was that maintaining the battery at its highest possible voltage reduces its life and stores maximum energy for potential damage. But no current is being drawn from the battery in this situation. I am proposing continuous charge / discharge cycles which probably reduce life quicker than the high voltage ?
 
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agraham

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I am proposing continuous charge / discharge cycles which probably reduce life quicker than the high voltage ?
I have had a Surface Pro 4 Windows 10 laptop on permanent charge for at least five years now with no problems in the belief that it is better (and easier for me) to do that rather than keeping running it down and recharging it. No problems at all so far, although as it is rarely used unplugged I don't really know if the overall capacity has reduced or not. But then if it is continually plugged in the ultimate capacity is irrelevant.

I would say that if you are worried about the safety aspects of Li-ion batteries then you should not be using one at all. If you are willing to use one then just use it as conveniently as possible and forget about any fancy charging/discharging/optimisation strategies - particularly if you can just plug it into vehicle power. If you are unlucky enough to get a bulging battery then you are just unlucky. I don't think you can rely on any strategy to mitigate the risk of that happening.
 
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Cableguy

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This has spiked my curiosity...

If I understand correctly so far, you are developing a device that is to be installed in a vehicle, right?
So my question is:
Will this device be continuous ON?! Like, even when the vehicle is parked overnight?

If the device does not need to be continuously powered on, and only needs to be on when the vehicle is in use (key in the ignition), then my advice is to take of the battery, and power the device through a circuit to allow for some safety feature for when the motor is started, and for a more "clean" way of powering it off.
 
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AHilton

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" What leads you to think short cycling is bad ? " Experience.

The specific rules about charge per cell is different between battery chemistries depending on if you're talking Usage, Storage and long-term Storage. For example, lead-acid should be kept fully charged (note: this does NOT mean leaving it on a full charge continuously), regardless. This would spell potential disaster (aka terrible explosion/fire) when we're talking about the lithium polymer batteries. You drop those down some V's even for moderate Storage (note: STORAGE not Usage) times. Lithium ion batteries it's not such a bad thing but it also doesn't really get you additional benefit, either. Not in the real-world. Especially considering you're not really using the batteries anyway. If possible, as agraham and Cableguy suggested above, get rid of the battery itself and you've saved yourself/customers the headache.

I started putting devices in trucks (firetrucks, police, ambulances) back in the early 90's and now into semi's since 2001. Keep the power simple.
 
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