Batteries---when to end it?

I was wondering when people replace your actual camera batteries (as opposed to replaced the battery in camera)? Do you wait for them to die outright? Is there any harm in continuing to use them even as their recharge performance dwindles?

My story, I have 3 LP-E6 batteries. One that came with my 7D, one with my 5DIII and one I bought as a back-up in 2011.

I set one aside to sell with my 7D (a friend wants to buy it but we are waiting) and I marked the battery I received with the 5DIII.

On my Florida trip, I noticed that one of the batteries that are from 2010 or 2011 (not the 5DIII battery) finally dropped to the single red bar in "recharge performance." This is a first for me. I continued to shoot with it and went through ~700 shots with plenty review time before it needed recharged again. So, the performance is still good.

So far, with all three LP-E6 batteries, my experience is that they pretty quickly (couple of months) went from 3 bars of recharge performance to 2 bars and stayed at 2 bars for years...until now.

I always carry a backup battery, so I should be fine. But I am tempted to discard the battery that has 1 red bar recharge performance and replace it with a newer battery.

Thanks....

If I understand this correctly, the bad battery gave you 700 shots?

I used to shoot indiscriminately when I went digital. Memory is cheap after all compared to the cost of developing film.
Now I seldom have a day over 700 shots. To much sorting, and I try to be selective. A battery that can do 700 shots is good for a day. I might be inclined to keep using it, even if I bought another as a spare for my own piece of mind.

I have batteries six years old now, I haven't paid attention to their strength but they seem softer than they used to be. It doesn't bother me because I have four and always a backup. That's enough to shoot heavy for three days without charging.

I would judge the need by how many days you have to go without charging.

Yep. My "bad" battery gave about 700 shots over about 3 days with plenty of in camera review and deleting.

Performance is still good. The thing that got my attention was the bar for recharge performance has turned from green to red. I guess another way to phrase this, have others had issues once batteries hit the 1 bar in recharge performance. It is a 4-5 year old battery.

My inclination is to keep using it but always have a back up. I may get a new battery just to have a newer one in the mix.