My phones speakers have crapped out and I’m getting a new phone. Rather than throw out the phone, can I use it as a permanent hotspot to provide access to a security camera at a remote location that doesnt have internet access? The phone is a Samsung S9+.
Answering my own question…
Yes.
Lots of hits using goggles. One is this;
What about the battery charging and discharge cycles. How would one manage that?
I wanted to do something like this with my One plus 3. But got scared I might have ticking time bomb if I left the phone on charging all that time.
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If I’m using it as permanent hotspot then I’m not worried about battery decay. The battery will act like a backup power supply. I’m more worried about it getting cold, but I think a small heating blanket will work for winter. It gets to - 45C sometimes.
I’m pretty sure the samsung has a very good battery charge maintenance program.
there’s a good chance you wont need to worry about the cold as leaving it on charge and draining it with the wifi hotspot will stress the phone hard enough to keep it warm… maybe even to warm.
battery’s don’t like being over charged especially for repeated cycles.
so while you could and can do it… you might want to do some stability testing first.
coz the last thing you want is to leave it unattended only to return to find out your responsible for a lithium fire.
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How would I do a stability test? I guess leave the phone plugged in and hook up a security camera to the wifi while I’m present? How long would be sufficient?
cant say mate it will depend on the current state of the battery.
and as to how long you want to test…
i would assume however long your going to leave it.
but even then there’s no accounting for next time.
it may be fine for a couple of days or even weeks and months use, but it could also go pop the next time you leave it for a few days.
your phone may have a battery tester… set it up at home how you will use it…
if after a few trial runs your happy that you aint seeing any issue then try it off site.
oh and i would remind you about putting cameras up in places they shouldn’t be.
it might seem a good idea to install a camera but you could end up breaking the law yourself, if you accidentally/intentionally breach some-ones privacy.
so check before you do anything. 
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Phone like to ignite if you leave them on a charger indefinitely
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Hmmm, perhaps I can put it on a timer.
Or if you leave it off the charger indefinitely. It’s a small sample size, but apparently Samsung sucks more than others.
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All Top companies test for that and build devices to withstand those temperatures structurally.
During Summers in India my One plus Nord switch itself off if as it get hot to touch after 45min of use as a webcam.
The camera processing video on it should keep the device warm enough to keep it in a working state during winter. ( Don’t know much about snowy conditions)
During spring or rains the moisture and humidity might cause more problems than summer heat. so keep it safe from the elements and it should be fine.
Last time I was thinking about the charging issue . I came up with a idea ,but don’t know if it works practically.
Using a smart switches or plugs that work with Home assistant. A script or program To check the battery level by using the Android bridge wireless debugging function, setting a chron job for every few hours and sending a command to the switch to charge the phone every time it discharges below 30% and stop charging at 80%.
But this was above my skill level so I dropped it.
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I have a feeling that would still put a lot of stress on the battery, camera will chew trough it in no time and you would be looking at several charge/discharge cycles daily.
I have two android tablets that are connected to the charger and have screens, wifi… 24/365. Not yet exploded! 
You can also buy a suitable fireproof box.
Or something of your own… A container with water, and in it a second waterproof container and only outside for power and antenna. Or sand instead of water.
and?..
like i said they can work days, weeks or months without issue.
and i would point you to the vid vivante posted.
the narrator clearly says its aging phones that have the issues for the most part.
the op is using his old phone… so for safety sake i thought it worth a mention. just in case…
I am fully aware of the behavior of the battery and the risks associated with it. It is worth mentioning, but it also makes no sense to panic. Many things can cause a fire and batteries are one of many sources.
Even old batteries that are badly worn out do not catch fire just because they are old. If we are talking about the famous Samsung phones burning, it is a problem with new batteries and their defect, not an effect of old age / wear and tear.
Yes, the battery is a risk, but in the case of OP it is not more than going to sleep and leave the device on the desk.
You must protect yourself in the event of such a fire. Both for its early detection and for extinguishing / limiting its spreading.
Houses / flats burn much more often from a faulty electrical installation and from a situation in the kitchen than from a battery.
Battery fire is very aggressive, but if we prepare a place for the storage of the device, we can survive the fire and not suffer severe losses.
Even on board the plane, you can survive a battery fire and the crew are ready for such a situation. But as everywhere, speed of reaction and the right way count.
There are at least a few ways to prevent a tragedy in the event of a battery fire, but they require motivation and $ from the OP.
However, the fact that you mention the threat is absolutely positive, but it is also always worth adding that it is not the end of the world.
Often the cause of battery ignition is physical damage or overheating, the source of overheating may vary and is usually external and not the device itself.
It is also known that a battery that is already swollen should not be used, because it increases the risk of its bursting and, as a result, it will immediately ignite.
The problem can also be very cheap replacements, which can sometimes just be total junk and a ticking bomb.
It is best to start by buying a solid large container that will withstand the fire and will not allow the fire from the battery to move to other surfaces.
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I don’t recommend old phones as security cameras. A real Wi-Fi security camera will have vastly superior performance in low-light conditions to a phone. Security cameras are so very inexpensive, it doesn’t make much sense to mess with an old phone… Seeing some for $20/$30/$40 on Amazon. They may have PTZ and other features you’d want, too. e.g.:
Root your phone, install Magisk, then install ACC as a module and configure it for the high/low battery percentages you want:
Many Android devices already have some sort of “battery protection mode” built-in:
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A bit of miscommunication… I plan on having a security camera on site. But there is no internet. So I want to use my phone as a hotspot to send the cam notifications to my personal phone. My old phone is a Samsung s-9+, and I’m pretty sure it has battery monitoring. The security camera I plan on using is a Wyze V3.
Or perhaps this one;
The general rules are still the same. Just to be safe, you can think of a fireproof container in case the battery ignites one day. At least to separate the phone from the environment so that it would not be able to light up anything else. Even an open metal basket…
As for the hotspot itself, android has it already built in, so you don’t even need a dedicated application. Alternatively you can consider a firewall like “NoRoot Firewall” and if you need automation / macros “macrodroid”.
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