Fail, Teardown: LG G Pro Lite Dual (D686) BL-48TH Battery Swelling

Aside: Given that I’ve got a PhD thesis to hand in on Thursday this week, what the hell am I doing posting blogs? Well, as it turns out, in-between putting-out fires, I need to recharge and it seems that posting a few more articles is probably the thing I need to take my mind off of my thesis so I can “reset” my motivation.

I’ve always made a point of carrying two phones with me – a phone-phone that I use for “phone” things, and a data-phone that I use for smartphone things. In fact, my data-phone was a direct evolution from moving away from tablets as I really didn’t see them to be as convenient as I would have liked.

Since my hassles finding genuine replacement batteries for my Samsung Galaxy SIII, it decided to die not-long-after due to an eMMC failure. The other phone at the time was this LG G Pro Lite Dual (D686), and it managed to tie me over until I found the right phone to take over. I’m not one to upgrade phones very often, and when I do, I don’t tend to buy the flagship models, so in the end, I got a Xiaomi Redmi Note 2 (which I still haven’t gotten around to reviewing).

It’s funny, because it was the decrease in battery capacity and strange run time issues with the LG that prompted me to buy a phone to replace the Samsung. Not long after, the LG started to follow the same path as the Samsung.


I noticed problems typing on the screen, and when pressing on the screen, the LCD would show a bruise spot right in the middle of the keyboard even when the pressure was applied elsewhere on the screen.


Removing the phone from the case showed the rear cover slightly lifted off the body with no real way to get it to close again.


Removing the cover showed the battery levering out of its position. Yep. The battery decided to swell, likely because of all these years of accumulated micro-cycling while sitting on the charger. I suspect that’s just down to how these phones treat their Li-ion cells, and how well they’re made.


Propping it against a straight edge makes the swelling clearer. It’s not catastrophic but it interferes with usability which is not good. Besides, any more pressure, and when the cell decides to vent, we might get a nice flamethrower … I’d rather not have that.


The battery was dated 21st November 2013, lasting 858 days (or 2.35 years) since it was manufactured. It’s a little disappointing, but it’s not quite as bad as my SGSIII experience. Before sending it off, I might as well strip it down and see its innards.

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The cell has a vent stamped into the lower left of the top (unmarked) side. The bottom side is marked LGTH4ZA4857, which indicates the cell is one of their own products.


Removing the top plastic covering shows the main battery protection PCB. It was very well secured to the battery, so I had to apply some force to tear it off, shearing what appears to be a non-resettable fuse in the process.


Nothing particularly special was noted, I suppose.

A Desperate Hack Attempt

I would be out of my phone-phone for a while as I waited for a new battery to turn up. I wondered if I could do something about it …

I still had the Samsung Galaxy SIII battery, and it had the same power pin-out as the LG battery. It was the right thickness too … but dimensionally, it was small.


Luckily, I had some unwanted disposable chopsticks. These are a wonderful material to work with – just like balsa wood, all you need is a hobby knife to work with this. Not five minutes later, I had a very secure mounting.


I tried to boot it up on battery, and it started but then shut-down immediately. Hmm. I connected it to the charger, and the reason was clear:


It appears that the thermistor connections, or the thermistor configuration is different on the LG battery. This is very likely as the Samsung battery uses the spare pins for NFC – and whatever it leaves the pin at (floating? tied to ground?) doesn’t make the LG happy.

But we also come to a very interesting result – namely, the stock LG ROM is missing a warning image for overtemperature.

I suppose, if I was desperate enough, I would probably tape over the thermistor terminals to see what happens, or try to rescue the PCB from the original battery out of the bin and do some measurements … but I’m really not that bothered. After all, my Redmi Note 2 is dual-SIM … and can handle being my phone-phone for a few weeks as a replacement battery arrives.

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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