use an old phone's battery in a newer phone! Do at your own risk!

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Use an old/cheap phone's battery in your newer phone! Woot!

My phone started acting up... It'd say it was fully-charged, but die without warning after less than 15 minutes. Plug it in, and the charge-indicator would say 60%. WTF?

Opened up the back and found that the battery was quite bloated.

I've had this phone for several years, and it was a refurb when I got it... so it's old enough that most stores don't carry its battery. To top it off, it's a weird make, despite being from one of the leading brands...

I needed a functional battery ASAP, but the only place carrying a replacement was towns away, and they wanted me to shell out more cash than for an equivalent phone, of today's standards.


But, I had a *really cheap* 'burner phone', prior, yahknow, before touchscreens... and it just happened to be the same brand. Would it work?

Some considerations:

Voltage: New is 3.8, old is 3.7 (Danger?)

Capacity: How do these things determine the charge-rate, when you can buy batteries of different capacities?

Pinout: If necessary, I could solder the darn thing to wire properly,.. But, the newer battery had four pins, while the older had only three. 

Turns out the fourth is for the 'near-field communication' antenna, which I've never used, and many people with tinfoil caps cut off, anyhow. So, ignore the fourth.

Positive and Negative were clearly labelled on both batteries, and in the same positions.

That left the second pin... in the old days of Li-Ion batteries, that'd be for a thermocouple, to monitor the battery temperature. Could I rely on their having used compatible thermocouples across a half-decade or more? Besides, in this more-sophisticated era, many batteries have 'smart' monitors built-in, communicating via serial-protocol which likely varies from manufacturer to manufacturer, if not with each model. 

I did an experiment: Plug the old battery into the old phone, blocking Pin2 with a piece of tape. As I recall (this was months ago), the phone would power-up, but not charge. I vaguely recall a message that the battery was damaged.

So, it seemed the odds were not in my favor, and I was about to give up... Was fiddling around with it and realized the friggin pinout not only matched, but the pins lined-up darn-near perfectly. So, I had to try...

(the black thing on the newer battery is the NFC antenna, clearly wired to pin 4)

A tiny bit of finnagling it in there, and a custom spacer did the job! (didn't even need a razor-knife, nor 3D printer!)

It powered right up... and even began charging. After some oddities with charging and capacity for a few days, it started functioning, well, I'd call it "reliably", and certainly better than expected. Been using it like this for well over half a year, now. WAY more functional than the bloated battery.

  • forgot The Kicker!

    Eric Hertz04/04/2018 at 17:48 2 comments

    The original battery, again, was claiming to be fully-charged, but would only last maybe 20 minutes when unplugged... then when plugged back in, it'd immediately show ~60% charge, which used to be plenty for a couple hours. 

    When it'd conk-out, there'd be no warning. Often, I'd be in the middle of taking pictures, the last would always be corrupt. But the videos that were cut short were the most frustrating... five minutes of footage lost, numerous times... 

    one time there was a very thirsty deer trapped between I-5 at rush-hour, and a really long fence... was trying to help it get to the lake, and filming... and lost all the footage, a good half-hour, due to a no-warning battery-fail. I never did find a way for the deer to get through the fence, and while I was looking, he disappeared... Thankfully, I didn't hear any honking nor swerving, and traffic was pretty steady, so I guess he must've crossed back over safely.

    Anyways, got to the point where I'd stop and restart my vids every couple minutes, so I'd only lose a couple minutes' footage, instead of the whole video... and that was doable for a while... frustrating, but apparently not frustrating enough to fix.

    The Kicker, though, happened a few days after I got the old battery from storage... The plan was in the works, but implementation was on-hold. Until, a few days later it just wouldn't power-up, at all. Even when plugged in. There was no choice, at that point, but to try the older phone's battery, and boy-howdy it was a relief to see that home-screen again... but to be able to take videos without it dying and corrupting them...? WOW!

    Later, I discovered something utterly-ridiculous about this phone: When it's plugged-in and powered-off, it takes more power to bring up the "charging" screen (and, stupidly, spin the vibrate motor) than a typical charger is able to supply to the battery before bringing up that screen. Thus, with a really-dead battery, it charges for a few seconds, brings up the screen, vibrates, then drops dead again before repeating.

    Sometimes it'd do this twenty times before gaining just enough charge to sustain thereafter. BUT, only with a high-power charger. With a regular dumb 500mA charger, it'd sit in that loop overnight, or longer, maybe never gaining enough charge to bootstrap *charging*!

    Then, to really top it off, the dang thing wont't function *at all* without a battery! So I couldn't even use it while sitting next to a power outlet! Talk about needing hackery just to use these things for the gazillion other purposes a tiny supercomputer could be used for!

    I'd thought about putting a switch before the vibrate-motor as well as the backlight LED, that might've helped... thankfully I didn't have to go that far, as the combination of the old phone's battery and a 2.1A charger (and cable) eventually got it working.

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