Best way to drain down a battery?
 

What is the best way, least amount of wear and tear, to drain down a battery? I need to do some test on charging

and is it good idea to drain down batteries every now and then? thanks

Depends on what kind of battery it is. Generally it's not a good idea to completely drain a battery, especially the newer ones like lithium ion or Nickel metal hydride. You'll just ruin them.

you build a resistor that drain about what you need and that's all.
you should not exceed the rated current on battery, since li-ion or ni-mh do not support very well fast discharge.
let's say you got a 7.2V battery rated 4800mAH. (or about 35W).
if you camera drains 17W, the battery should be ok for 2 hours.
to simulate this, you build a resistor that drains 17W under 7.2V (or about 2400mA).
simple way to do this is to use a light bulb rated about as needed.
the problem is this should not be left unnatended, since deeply discharging such battery is very bad.
you can find commercial product that can charge and discharge battery even on several cycles.
Sony sells high end charger that can discharge battery first before charging. i think you can probably find that for any brand.

thanks, Yes I have 4 li-ions for Sony HD.

Giroud, did not understand much there and am not going to build anything, but what about just playing a tape through a few times? (although its wear and tear)

But Ben thinks it's not a good idea anyway.

Any links to buy this charger, discharger?

this is all becuase I have one battery that does not seem to charge well , and I'm not sure if its the AC adater, camera, or that one battery, so I have to test, and all my batteries are full.

Some research into lithium ion batteries would be advisable. Li-ion batteries should never be discharged past a certain voltage output. Doing so can permanently damage or destroy the battery.

Li-ion batteries can go into what's known as deep discharge. Batteries that are in deep discharge can take an unusually long time to recharge, sometimes measured in days. If a battery is too discharged to be recharged, it is useless.

If a battery is not lasting as long as normal, or doesn't recharge properly, you may have discharged it past a recommended amount. Generally li-ion batteries are used in tandem only with equipment that can sense at what point the battery has been discharged (via voltage measurement) and will not function if the battery is near/at a certain point. If you want to use a battery to its full safe discharge, you can probably assume that Sony has built that functionality into their cameras. Simply leave it on for a while (no need to run tape) until the camera automatically shuts off.

Unlike other batteries, Li-ion lifespans actually depend on their age from the manufacturing plant, not charge-discharge cycles or shelf-life.

Do not discharge your li-ion battery with anything other than what it is supposed to be used with.

Thorough experience with Li-ion batteries in my engineering class during the construction of a hovercraft taught me a lot about the volatile chemistry of Lithium ion cells, so be very careful when experimenting...

I agree with Ben.

Just put the lens cap on your camera, and leave it on without running the tape. Be prepared to wait for quite a while, probably hours, depending on your camera.

I highly recommend that you avoid using a simple resisitor or light bulb. The feature that shuts off your camera when the battery gets low is designed to save your battery.

In my opinion, it is not a good idea to discharge a lithium-ion battery every now and then. I know of no reason why this would be a good idea.

Kevin, send us your batteries, we will cycle them once on our tester and return with the verdict.

thanks Alex, will bookmark your site