I've been away for a few weeks and prior to that not used the drone for a month or so... today I come to use the P4 and see my two batteries need charging. One charges OK, but a spare I had (which is literally just one week over a year old), would not charge.
All 4 lights lit up in sequence, the a single light flashed and finally it powered itself off.
Closer inspection shows the battery seems to have leaked, and there's a definite slightly acrid smell when putting my nose really close to it.
Sadly it seems batteries only have a 6 month warranty (I would've thought at least a year to be honest!) So, that's £120 down the drain and now need to spend the same again.
Here's a couple of pics.

I don't know what went wrong... Did the phantom heat up too much? I have the Phantom 4 and have had it for some time and I have never seen this problem occur. I would try to contact a member of the DJI team and possibly they can get some help for you. Sorry about what happened.

The battery wasn't in the drone at all (another battery was), it had been stored in the backpack along with the drone. Not used for maybe two months I guess.
I didn't take any notice if the battery was already failed prior to plugging it in to charge straight from storage.

I chatted with some support person online, and is how I know about 6 month warranty,

This is a good reason not to stock up on a lot of DJI batteries, imho.  If you let them sit, they may not charge at all later on.  Plus, warranty is very short.  The RC warranty is one year but the battery in it is what? - and then you need to send it in for replacement too.  New Cendence RC has user-changeable batteries, but $999 though for that RC.

My local  hobby shop owner claims some of his Li-Pos he uses are a decade old now and still working.  They are plain generics without all the electronics on them as with the DJI ones.  He has a smart charger and uses it for his electric powered planes and helicopters Li-pos.  He says the kids all use what he calls a "Car charger" and cooks them to death rather than using smart charger on them so he sells a lot of Li-pos to them.

I agree with fansa84fe8a4. You should not store lots of batteries, however, this should not have happened.

Definitely a leak here. Probably as new. I wouldn't breathe to much of that.

I'm sorry to hear. To clarify, what kind of climate was the backpack stored in? Did you have a hard landing at any point?

DJI-Jamie Posted at 2017-4-25 20:35
I'm sorry to hear. To clarify, what kind of climate was the backpack stored in? Did you have a hard landing at any point?

The backpack is in my bedroom cupboard, which I guess would be classed as room temp (hovering between 16-20 degrees Celsius).
I've had no hard landings at all with the drone. I'd go as far to say the battery has had a maximum of around 15 charges as I'm an infrequent user of the P4.