Can I wire a smartphone to bypass its battery? - Page 1
Forum section: electronics / repair

author: Starglider
author_rank: Contributor
timestamp: May 28, 2019, 09:09:27 pm
content: Hi, I use a Google Nexus 5 smartphone as the hub for my smart home. This means I leave it plugged in all the time. However twice now the battery has expanded and popped the back off the phone.I don't really need a battery in there at all but if I remove the battery the phone will no longer boot when connected to the mains.Is there a way I can hotwire something inside so it will completely bypass the battery but will still boot up? I'm experienced with soldiering & multimeters.Thanks!

author: Starglider
author_rank: Contributor
timestamp: May 30, 2019, 11:59:15 pm
content: BumpSent from my SM-N950U1 using Tapatalk

author: coromonadalix
author_rank: Super Contributor
timestamp: May 31, 2019, 12:56:07 am
content: maybe something like a supercapacitor ??, if your battery bust, you may have a charging problem, or maybe you have a non genuine batterieI had this phone, never had any problems, was connected at least 12 hrs a day to play music ...oh normally you have 3 pins for the battery : a positive, a negative and a sense pin / charging feedback pins or maybe a tap in the battery configuration, check a busted battery to see how its made

author: DaJMasta
author_rank: Super Contributor
timestamp: May 31, 2019, 01:14:55 am
content: Can you just remove the battery? All of the phones I've had with a removable battery can be powered up under just external power with no issue.

author: Starglider
author_rank: Contributor
timestamp: May 31, 2019, 02:43:51 am
content: Quote from: DaJMasta on May 31, 2019, 01:14:55 amStrangely it won't boot when I do thatSent from my SM-N950U1 using Tapatalk

author: wraper
author_rank: Unknown
timestamp: May 31, 2019, 03:04:06 am
content: You need to salvage circuit from a battery and connect 3.6-4V PSU where battery element was originally connected to it. You won't need any charger connected then. It's not simply the case that phones need an energy storage. Usually they won't power ON even if voltage is applied to battery power pins, but data/temperature sensor pin(s) left not connected. You can get 4V from say original charger by slightly modifying feedback circuit in it.

author: wraper
author_rank: Unknown
timestamp: May 31, 2019, 03:06:20 am
content: Quote from: DaJMasta on May 31, 2019, 01:14:55 amDunno which phones you had but I haven't seen a single one which works without a battery installed.

author: DaJMasta
author_rank: Super Contributor
timestamp: May 31, 2019, 03:59:54 pm
content: Quote from: wraper on May 31, 2019, 03:06:20 amSamsung Galaxy Nexus, LG G3, the only two smartphones prior to my current one I've owned. Both have removable batteries, though, which could be the difference.

author: wraper
author_rank: Unknown
timestamp: May 31, 2019, 04:08:13 pm
content: Quote from: DaJMasta on May 31, 2019, 03:59:54 pmI can say than not a single Nokia made in 2000 and later worked without a battery. Previous likely did the same but I haven't chance to test them.

author: magic
author_rank: Super Contributor
timestamp: May 31, 2019, 09:55:23 pm
content: If the battery is non-removable, does it even contain any electronics or is it just a bare cell which could be replaced with any common lithium cell?

author: KaneTW
author_rank: Frequent Contributor
timestamp: May 31, 2019, 09:59:31 pm
content: Depends. Check the pin count.

author: wraper
author_rank: Unknown
timestamp: May 31, 2019, 10:36:28 pm
content: Quote from: magic on May 31, 2019, 09:55:23 pmNo phones with bare lithium cell do exist, unless it's a some sort of special counterfeit crap. They have 3 terminals as minimum and protection circuit built in.

author: bitseeker
author_rank: Super Contributor
timestamp: June 01, 2019, 04:25:10 am
content: I wonder if it might be possible to keep the battery in, but make the protection circuitry terminate charging at a lower voltage to stop it from overcharging or even maintaining a high state of charge. Some laptops (ThinkPad) have software-configurable chargers. I'm not aware of similar options for smartphones or tablets.

author: Starglider
author_rank: Contributor
timestamp: June 01, 2019, 04:44:43 am
content: Well, I've ordered a new OEM battery. Simpler!

author: Mr.B
author_rank: Unknown
timestamp: June 01, 2019, 05:37:12 am
content: Quote from: bitseeker on June 01, 2019, 04:25:10 amAFAIK,Samsung Galaxy S series from 8 upwards had settings options to prevent charging over 80%.edit: Forget that... Getting confused with my HP laptop.

author: soldar
author_rank: Super Contributor
timestamp: June 01, 2019, 12:19:54 pm
content: My experience with devices in general, not just phones, is that you can connect an outside PSU to the battery terminals so it thinks it has a battery connected. The third contact for the (temperature?) sensor can easily be connected to a resistor. Just measure the resistance on a battery at room temperature and put a similar value. I cannot remember any time this has not worked for me.In fact, I have right here an (old) video cam which has some kind of battery that is not to be found anywhere. It seems to be a badly designed BL-5C so that the contacts are shifted 2 mm towards the center. In the photo you can see the real BL-5C at the bottom which will not make contact with the camera contacts. Since I cannot find batteries I just prepared a dummy battery with a strip of PCB for the contacts and I power it from outside. Even though the battery is nominally 3.7 V I found I can use a 5V USB adapter and it works very well. The camera thinks it has a full battery all the time.

author: Starglider
author_rank: Contributor
timestamp: June 02, 2019, 06:16:52 am
content: Thanks for the problem is the connection on this more modern battery is microscopic and not like a camera battery.

author: soldar
author_rank: Super Contributor
timestamp: June 02, 2019, 10:25:14 am
content: Can't you use the connector of a discarded battery?

author: Siwastaja
author_rank: Super Contributor
timestamp: June 02, 2019, 11:11:54 am
content: Quote from: wraper on May 31, 2019, 10:36:28 pmThis third terminal is sometimes just a fixed resistor used for super-simplistic identification; sometimes it's a thermistor output, for measuring cell temperature. Some exotic batteries, think about Sony products, did include anti-copy bullshit measures on the third pin, but that seems to be more of an exception than a rule (and is actually related more to copy protection, than to battery safety.)Additionally, they tend to have fuses, mechanical or PTC.Otherwise than that, they tend to be "bare" cells, because it's simpler to have the voltage protection circuitry on the main PCB of the phone.For modern phones with batteries the user cannot replace, it makes even less sense to add separate protection boards, or even excess fusing, just a bare pouch cell is typical. Why would they have anything else, is beyond me.

author: wraper
author_rank: Unknown
timestamp: June 02, 2019, 12:04:53 pm
content: Quote from: Siwastaja on June 02, 2019, 11:11:54 amYes, 3rd pin often is just a termistor or resistor, like it was in almost all Nokia phones (BSI). But otherwise you are wrong, all of them have protection circuit which includes MOSFETs to cut off the cell if something is not right, like when battery is overdischarged.

author: NiHaoMike
author_rank: Super Contributor
timestamp: June 03, 2019, 03:27:30 pm
content: In the Perk mining days, a common trick was to replace the battery with a 5V power supply and a series diode to drop the voltage to about 4.3V. That 5V power supply could be the USB input or for a Perk mining cluster with dozens of phones, it was common to recycle an older ATX PSU with a lot of amps on the 5V. Some phones also need some trickery with a resistor or salvaging the board from the battery.