So today I was shuffling through all my JP1 accessories and found a dead Jolla battery. I tried to revive it by putting it inside my phone and then plugging a charger to my phone. Doesn't work. Tried several times. Then I had an idea: What if I first plug in a charger and then put the battery inside Jolla?

So I put the battery inside Jolla, and the charging light briefly lit for a split second, and then it changed to red-blinking (meaning it won't charge). Tried again and now after brief charging light the led turned to constant yellow. It was in this state for maybe 10 seconds and then the led changed to red blinking.

Then I tried again, and lo and behold, it started charging and booting into SFOS!

I turned off the phone and it started blinking red again, so don't do that. I did get it to charge without booting into SFOS though by trying the trick once more.

Sharing this as maybe other people have dead Jolla batteries too!

PS: The battery I revived had been dead for a year.

EDIT: No guarantees that this doesn't break your phone (I don't know the dangers of this method).

Even if your battery might work now there is no guarantee that it will not expand or explode later. Believe me i've seen a battery expand *after some* charging cycles *after* reviving it in a similar way (Nexus 4). In this case it "only" broke the display by expanding but i don't want to know what else could have happened.

If your phone doesn't want to charge your battery anymore it is probably for a good reason. Especially if it's been dead for so long.

Well, I remember how it happened in the last summer: my old Jolla got in a boot-loop and completely drained the battery. Wouldn't charge after that.

I have also rescued one battery from that as it somehow miraculously started charging after-boot-loop drain (had to plug and unplug the charger several times however before it accepted current). The battery worked fine after that and that battery still works.

Do you think the time it has spent completely drained makes the battery dangerous to use?

EDIT: I also observed today that when you put a completely drained battery in a Jolla phone and it won't charge (led blinks red), next time you put a battery in that it agrees to charge the phone always boots into SFOS. It doesn't stay in the charging screen. Don't know if this plays any part in this.

It becomes more dangerous the less voltage the battery has before the recovery afaik. Everything below 3V is not good for lithium-ion batterys. So time/self-discharge plays a role.

Thanks for the info!

I guess there's nothing to do to reduce the risk of battery expansion/explosion if it indeed has been damaged by the long time it's voltage was below what the phone would accept...?

Most phones require the "flat" battery to still have some charge that will allow the charing controller to operate and charge the battery. The trick you did most likely let the battery to get some initial charge that was enough to start the charging process.

Your battery might be ok now, but you need to be careful with it, especially during charging cycles.

It might be safer to do it with a specialised charger for lithium batteries.