I have a 12 year old Siemens S6 cellphone that I keep as a museum piece - haven't used it regularly for eight years now. Original battery still working but probably not for long. I luckily found replacements batteries on the Internet at less than £4 a piece so I bought two...

but how are they best stored? Uncharged as from the supplier or fully charged (and recharged now and then)?

Just be careful with 'cheap' rechargeable mobile batteries.

Many come from chine, and dont have overheat protection and several have exploded killing people. Including one guy who's motorola ended up embeded in his chest from where he had it in his shirt pocket!

Another guy, hong kong IIRC, almost lost his little man too! :eek:

I no longer keep my phone in my trouser pocket.....

How to store Li-Ion batteries

I Googled using exactly those terms - lots came up.

Apparently, concensus is to store them at 40% charge (how you're going to determine that could be interesting )

Example link here

Chapter 10: Getting the Most from your Batteries

I looked into this re: laptop batteries a few months ago. IIRC storage while part charged (40% springs to mind) was best for laptop batteries. Try google for some info.

Edit: lol, Val beat me to it but at least I was right

Thanks, everyone. Seems as if I should charge them partially and leave them, then - maybe that's why the old battery have survived so long, these last years when the phone has just been a spare it has been charged maybe once a year.

And yes, I'll remember the warning for cheap batteries. It says on the box that it has overheating protection, but I won't leave it on charging overnight just in case...