Tablet with battery puffed up will not turn on without battery - revival? - Page 1
Forum section: electronics / repair

author: r0tati0n
author_rank: Newbie
timestamp: January 14, 2021, 02:50:12 pm
content: I have a cheap Lenovo tablet.The glass bezel came off because the battery puffed up.Despite the puffed up battery the tablet turns on, when connected to power via USB.I opened the tablet and removed the battery and closed it again.But now the tablet does not turn on when connected to USB power.Is it possible the tablet needs a battery to run, even if permanently used on USB power?Is there a way to get it running again, preferrably without a battery, as the tablet stays stationary?

author: fordem
author_rank: Regular Contributor
timestamp: January 14, 2021, 03:01:32 pm
content: It is possible to wire the power circuit through the battery connector to prevent a battery powered device from functioning without the battery, and it might be possible to add a jumper to circumvent the feature - the real question does the battery do anything else besides powering the device - for example regulate the voltage.You would need to figure out how that battery is wired and which pins to jumper, and be willing to risk damage to the device.

author: CJay
author_rank: Super Contributor
timestamp: January 14, 2021, 04:55:57 pm
content: Yes, entirely possible it won't work without one, some smartphones are the same, you can't run them without a battery.

author: aqibi2000
author_rank: Regular Contributor
timestamp: January 14, 2021, 06:21:47 pm
content: What is the voltage you are supplying?Single cell ~4.2V, when you press boot does the current draw increase to even attempt?Can very easily just be the psu current limit dropping the voltage.

author: Runco990
author_rank: Frequent Contributor
timestamp: January 14, 2021, 08:10:57 pm
content: Try powering on the tablet and THEN unplugging the battery. If it turns off, it's current limited.If it stays on, it's a lock out.

author: r0tati0n
author_rank: Newbie
timestamp: January 15, 2021, 04:03:20 pm
content: I used a 3A 5V power supply as well as a beefy power bank capable of 5A, no boot.As the power bank powers down (LED go out if no power is drawn) I think the tablet draws some power for a second (enough to wake up the power bank) and then drops to zero.I dont think I want to plug in the battery again, as it puffed up quite heavily. Easily 5 times the original thickness

author: Renate
author_rank: Super Contributor
timestamp: January 15, 2021, 05:08:19 pm
content: Battery packs connect with a multipin connector.There is (almost?) always a single/dual red wire and a single/dual black wire. That's power.There can also be wires for almost anything else: 10 k thermistors, fixed resistors for ID, BMS ICs.Depending on firmware, some devices refuse to boot without a valid battery.What you do is take a bunch of tape off your battery pack until you see the tiny strip PCB that is on the top.This attaches to the actual battery using the battery's foil tabs.Break the tabs, recycle the leftover battery cell, solder your power suppy to the PCBs terminals.If you have a good USB supply, try connecting that instead of your PS through a 1N400x diode to drop it down to a reasonable battery voltage.If you have problems with it booting correctly throw an electrolytic on the 4.3 V side of the diode.

author: Jay Kominek
author_rank: Newbie
timestamp: January 15, 2021, 05:35:26 pm
content: Just as a data point, I've seen some lipo-powered consumer electronics that have an instantaneous draw of >10A on startup. You try to hook them up to a power supply with some reasonable wires, and the voltage drop across the wires will cause it to brownout on startup, even if your bench supply can satisfy the current demand.They could only reasonably work when connected to a battery by 2cm wires, even if you circumvented any of their battery detection stuff.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 16, 2021, 02:58:55 am
content: Add a 1N400x diode from the USB supply to what was connected to battery positive, was once well known as the "Perk miner trick" as it was once done to run dozens of cheap smartphones from an old PC power supply for Perk mining. (You can also use a direct connection if you're feeling really adventurous.) If it still doesn't power up, you might have to salvage the circuit board from the battery and connect it as well to fool the device into thinking it still has a battery connected.Or add an extra power connector and that will let you still use the USB connector for OTG if your device supports it. You can even do both to get the best of both worlds - you can power it from the DC supply or the USB input.