Near-dead Canon batteries - do you short them out?

Say you want to do an imaging session, and know your Canon battery is low on juice. Apparently, if you put that battery on charge, the only life you will get is the percentage "space" to be charged in it, thus the previous remaining charge in it is effectively dead. Is there a way to short circuit the battery to drain it completely before putting it on charge for maximum endurance?

Seanie.

I'm not too sure that memory charge applies to Lithium Ion batteries.
You could however put a resistor across the batterys terminals and drain whatever charge is left in it. To determine the resistor value use V=IR. Where V is the battery voltage (nominal) and I is the maximum current it can supply. R will then be the resistor value you use.
However I wouldn't do this unless you are finding that the battery you have wont take and hold a charge (if thats the case your probably better buying a new battery anyway). All re-chargeable batteries have a finite lifespan and can only be re-charged a finite ammount of times. Also avoid re-charging the battery until you really need to and keep a spare fully charged one ready in case you need it during a session.

The batteries are both new. I was just thinking from the point of view if having a long observing session, and wanting to plan to get the most from the batteries in advance.

Nickel Cadmium (Ni-Cad)batteries exhibit this so called "memory effect".
It's not really a "memory"..it is your battery dying.

It is irreversible chemical destruction within the battery caused by it being kept charged up and not regularly discharged fully before recharge.
(Which is why chargers have a "discharge" setting.)

This only applied to Ni-Cads.

Lithium-Ion or Lead-Acid batteries have different chemistries and thus this does not apply to them.
Fully discharging Lead-Acid batteries can destroy THEM!
With all batteries: RTFM.

The batteries are both new. I was just thinking from the point of view if having a long observing session, and wanting to plan to get the most from the batteries in advance.

Seanie,

I can make two recommendations which I implement quite successfully:

(1) turn off the preview mode for your camera's LCD ... the greatest consumption of battery power is the LCD screen

(2) get a battery power pack which allows you to load and use two batteries at the same. I can get nine hours of CONTINUOUS use with two 1800mA batteries loaded into my pack

Useful replies there, thanks guys. Peter, I didn't know that about NiCad batteries, but I was pretty sure some type of rechargeable had memory charge. Anto, that "Battery grip" for the Canon is on my wish list, I just haven't got round to buying it yet!