Tablet battery suddenly working again.  What did I do right? - Page 1
Forum section: electronics / beginners

author: Peabody
author_rank: Super Contributor
timestamp: May 29, 2019, 03:45:19 am
content: Since this ended well, I wanted to recount my adventure with the battery of my 5-year-old tablet in case it might be useful to others.I started having trouble with charging a few days ago. Even when the charger was plugged in, I would slowly lose ground on percentage charge if the tablet was on. And if it was off, but plugged in, it would only gain a few percentage points overnight, which was completly atypical. I tried another charger, and checked voltage and current under load on both, and both were fine.When the percentage charge dropped below 50%, I removed the back cover of the tablet, and tried disconnecting and reconnecting the battery, just in case something wasn't connecting well, but that didn't help. The bottom line was that the tablet wasn't drawing enough current from the charger to both power the tablet and charge the battery, and there was nothing I could do to change that. It turns out the processor is running, and warm, even when the tablet is off but is plugged into the charger. It's cool only when off and not plugged in.My final attempt was to disconnect the battery and leave it disconnected for 30 minutes, just to make sure all the caps were discharged and there was nothing left in ram, and to make sure the tablet would do a completely cold boot. Then with the tablet still off, I plugged the battery back in and waited another 30 minutes. Then I plugged in the charger, with the tablet still off. At that point it was drawing about 250ma, but after a while I noticed that the processor was barely warm., whereas before it would have been drawing about 500ma, but the processor would have been very warm, and no charging would be taking place. So I thought - well maybe it's actually charging now.So I left it charging overnight just to see if it would fully charge. And the next morning it was drawing about 50ma, still barely warm. But it was 100% charged! Battery voltage was 4.1V, up from 3.65V before.I have no idea what was wrong, or why it's working now, or how long it will work, but it appears the battery itself is just fine, despite its age. I should say that I have recently done a ROM upgrade, but the battery charged fine for a while after that, so I don't know if there's any connection.Anyway, I see on Youtube that this non-charging phenomenon happens fairly frequently with both phones and tablets, usually leading to replacing the battery. But it might be worthwhile to try this longer battery disconnect before ordering a new battery. It may not be a battery problem at all. No cost to give it a try, and maybe jiggling other things around, disconnecting and reconnecting them just in case.Attached is a pic of the battery connector. I have two black wires, two reds, a blue, a white and a yellow. The reds are B+, and the blacks are ground, but I don't know what the other three are for. Temperature maybe.I don't think it matters, but the tablet is a Hisense Sero 7 Pro from back in the day.Please post if you have an explanation for this. I have no idea.

author: Bud
author_rank: Super Contributor
timestamp: May 29, 2019, 04:46:49 am
content: I did the same to my nexus tablet after reading that might work, and it did. Disconnected the battery for a couple hours, reconnected and it started charging again. Probably that reset some circuit somewhere.

author: Peabody
author_rank: Super Contributor
timestamp: May 29, 2019, 09:07:52 pm
content: So it's a thing. Well that's good to know.