suck battery to zero

Yes- they step it up to more like 3V in most cases I think. I just got an MP3 player for my kid that runs off of a single 1.2V NiMH AAA cell for hours and hours.

Best regards, Spehro Pefhany

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Word of advice....if you don't want to spend the money on rechargables get Alaklines! Don't waste your money on Heavy duty batteries. Yes they are cheaper but last like 2 mins hahaha

Hey Spehro.

Isn't that killing the rechargeable batteries to run them down that far? IIRC, the discharge rate of any battery is non-linear. They typically peter out way before 0v.

Maybe NiMH can be functionally discharged to zero, dunno. I've been working with a lithium-ion design for it's good temperature range. Typical Li-ion cell voltage ranges from 4.100v +/-1% charged to to

2.5v "discharged", with voltages outside these ranges being "Very Bad"(R). So, stacks of these batteries must use some kind of charge equalization circuit or individual charger, otherwise risk overcharging and destroying a cell. Constant-current charging methodology doesn't help in this regard. Then cells under 2.5v must be trickle-charged to gently regain capacity... batteries sure have grown complex over the years... :)

-M

Definitely! =)

/A

To be pedantic (and it matters here), a battery is two or more cells, normally connected in series. It is definitely a Bad Thing to run a battery down to zero, as one cell of that battery will probably reach zero before the other(s), and as the other cell(s) continue to discharge, the weakest will be recharged with reverse polarity.

If you are just dealing with a single cell, this reverse charging can't happen (but it probably isn't good to discharge a cell to zero anyway...)

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Deep discharge of NiMH batteries is NOT recommended-- it can damage the battery. You get hardly any additional operating time below the recommended 1.0V per cell end voltage anyway, so it's best to actively shut down the circuit at about that voltage. Nominal voltage is 1.2V per cell. For long life per charge- use a high capacity cell (you can draw 1.5A for HOURS from modern AA cells) and design your circuit to use as little current as practical. For long battery life- follow all the battery manufacturer's recommendations.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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To nitpick the original point, with a constant power load, you can't generally run the battery down below half its original voltage. Because at that point, if you try to keep maintaining the same power out, the voltage just collapses to zero immediately.

But, going down to 0.7V (compared to say 1V) can give significantly longer run-times, at low power levels with alkaline cells.