To best maintain the functioning of the standard, rechargeable Lithium ion batteries in modern cameras, should the battery be used until the camera shuts down?
Some types of batteries have memory and their effectiveness is reduced if they are not fully charged and then used until fully discharged each time. (NiCad are an example.)
Are modern Canon cameras and batteries designed in such a way that the camera powers off at the optimum time towards the end of the batteries charge, minimizing the impact of memory on the battery? Or do Canon cameras by default let the battery become run down in such a way that the performance degrades substantially?
Might it be better to repeatedly partially discharge and then fully recharge the battery, than to fully discharge and then recharge the battery?
To extend the life of the battery, is it best to store it at a charge of up to 70%?
if you are using AA or AAA batteries, I suggest you look for a charger with maintenance functions, it costs about 30~50 $ but it makes your batteries last and younger :)
this is not the model I have but you may look at the features
Lithium batteries are almost free of memory effects, what will degrade the performance of the battery over time are build up of chemicals due to irreversible chemical reactions. If the battery is charged or discharged close to or beyond 100% charge state or close to or below 0% charge state, then you'll get a lot more of the irreversible chemical reactions in the battery. These irreversible chemical reactions are minimized between about 30% and 40% charge state. This means that it is best to store and use the battery near about 40% charge state.
The problem is then that it's not really very practical to only use your battery from 40% till 30% and then top it up to 40% again. You'll have to carry many batteries with you, if you want to do that, and the cost of all these extra batteries needs to be taken into account as well. But in principle, doing only one tenth of a charge-recharce cycle from 40% to 30% and back will lead to much less battery degradation per full charge cycle compared to doing full recharge cycles from 100% to 0% and back.
I use two batteries, I store one at about 35% charge, the other one is ready for use at 50% to 60% charge. When that battery nears 35%, I charge the other one to somewhere between 50% and 60% and I then interchange the batteries. I will only charge one or both batteries to 100% if I plan to take many pictures.
For a camera battery, the best advice is possibly to just not worry about the battery. Charge it when convenient or when you require it - simple as that.
As Count Iblis has stated, lithium batteries do not suffer from a "memory effect" - if anything, a complete discharge would be worse than charging when full. The optimum charge level for storage is around 50% - in a freezer, packed free/away from moisture.
Now there are some points worth keeping in mind:
For further reading, the Wikipedia article looks like a reasonable source (upon a quick glance): http://en.wikipedia.org/wiki/Lithium-ion_battery