I am using Dashboard on an old Nexus 9 tablet with Fully Kiosk. I noticed a bulging in the case which I attribute to an overheating battery. The tablet is mounted to a kitchen cabinet with Velcro strips. This also has occurred with an old Motorola Phone in the past. Does anyone else have similar problems?
How can I prevent this in the future?
I have configured Fully Kiosk to shut off the screen after 120 seconds and turn it on with motion.
Here are some photos:
Wow. That’s no fun - sorry to hear that. 
Fair warning for this post… your typical disclaimer applies that I don’t have expertise in battery design or charging circuits, so everything here on down is just from my research online and personal experience.
From what I understand, it’s usually related to either a faulty battery or faulty charging mechanism.
That being said, reading through some of the Quora answers linked below, several of the people mention that it’s a potentially hazardous issue to keep using devices in which the battery has started bulging.
Here’s a few snippets from answers on Quora:
Bulging batteries mean only one thing- buildup of gas inside. The gases are produced due to electrochemical oxidation of the electrolyte. Such oxidation occurs usually due to overcharging of the battery due to a faulty battery, or faulty charging electronics in the phone or battery charger.
Source: https://www.quora.com/What-would-cause-a-phone-battery-to-bulge-in-the-middle
and
First of all, if you are using a standard phone charger like the one that came with your phone, this should not happen , no matter how long you leave it on the charger. When a phone reaches 100%, normal chargers stop sending current to your phone.
That being said, if a lithium ion battery is overcharged , that is, too much charge energy is delivered, then it can swell up. Normal Li-ion have a maximum upper voltage of about 4.2-4.3 volts. Your charger should cut off MAX when the battery is in this voltage range, if not sooner.
Source: https://www.quora.com/Why-do-mobile-batteries-swell-up-with-excessive-charging
When lithium-ion batteries are over heated, over charged, or simply failing due to old age, it’s possible for the inner cells of the battery to outgas a flammable electrolyte mixture
Source: https://www.howtogeek.com/244846/what-to-do-when-your-phone-or-laptop-has-a-swollen-battery/
It sounds like the experts are saying this shouldn’t happen in a properly designed and functioning device+charger, but that things do wear down and break over time. I would hazard a guess that means that older devices would be more susceptible to this kind of issue… and that constant charging increases the risk - at least in the case that the preventative overcharging circuitry doesn’t work as expected.
For the first issue related to the age of devices, I guess the only real solution here is to not use older devices which isn’t always practical!
For the second part around constant charging, I’ve seen some people put their tablets onto a smart outlet and only charge the tablet as needed. Either charging it at specific times for a specific duration based on their experience… or getting fancy and using something like Tasker to only trigger the charger when the battery level gets low.
Thanks for your research. I’m going to toss this tablet. I need to find a new one for cheap. I’ve tried the Fire tablets, but they don’t work well in Kiosk mode.
The Fire tablets are a really good price/performance ratio, but as you noted they have one sticking issue with Fully Kiosk that you can’t put them completely to sleep unless you want to manually unlock the screen.
With normal Android tablets, Fully Kiosk Browser can turn the screen off, turn the screen on, and unlock the screen. On Fire Tablets, Fully can do all the above except unlocking the screen.
So that means that if you choose to have it turn the screen off on a Fire tablet, then you will have to manually unlock the screen.
As a workaround, many people leave their Fire tablets on 24/7 and either have Fully change to a screensaver (images, calendar, etc) or go to a completely black/dimmed screen. While this works OK in some situations, I can see how it’s not ideal for some. Especially considering the issue you experienced with your Nexus 9, I can understand being trigger shy with leaving a device on all the time!
A popular alternative to the Fire tablets in the Android space is the Galaxy Tab line of devices. They aren’t nearly as ‘cheap’ as the Fire tablets, but Samsung is a pretty well respected manufacturer in the space. Their Galaxy Tab A line is reasonably priced and I’ve seen a number of people use them for dashboards. The S line is a bit more premium with an OLED display and has a more premium price tag. I haven’t personally tried either of them, but it’s something to consider.
I’ve also seen a few recent mentions of the Huawei Mediapad line as dashboard displays in various Facebook groups, but haven’t tried those personally either.
Let us know what you end up going with!
I found a good deal for $66: https://www.amazon.com/gp/product/B018URWWLE/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1
Yes, the Nexus 7 is a refurbished 2013 model but is probably a better tablet than the Nexus 8 it replaced. Screen isn’t very big, but works as a dashboard fine. And about the same price as a Fire Tablet.
