What % Charge to Store 9 Cell Battery at?

[IBMorBust]

I did a search here, and the most common answer is appoximately 40%.

2 questions, though:

1) Why 40%?

2) For how long will the 9 cell battery stay at that level without concern?

This is for my T42. I use a 6 cell battery most of the time, but I take both batteries with me (usually) when I travel.

Thanks in advance for any feedback.

[Leon]

Current knowledge indicates between 40-50%. Don't know the exact reason maybe others can enlighten. If you travel less often than every few weeks, I would store it in the fridge, at 50% charge. It should be stored in a sealed plastic bag that contains a desiccant (available at any hardware store).

[Leon]

Update: I today removed a battery that was put new in the fridge with 40% charge last July (going on a long trip, and need both). The charge, when put back in the machine today, was down to 14%. Design capacity, 47.52. Full charge capacity 44.12.

Summary: A new battery, stored under somewhat optimum conditions for about 9 months, lost about 65% of its stored charge, and about 7% of its design capacity.