Re: Extending the Life of a Rechargable Battery

Keith Williams wrote:
In article <0%J2f.9286$zQ3.8332@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>, robertbaer@xxxxxxxxxxxxx says...

benn686@xxxxxxxxxxx wrote:

Ive heard its better for the life of a battery to charge a battery to
full capacity, use it until it drains completely and then fully
recharge it and so on.  I heard the battery will go bad faster if  you
partially charge, discharge more frequently.   Is this true?  Does it
depend on the type of rechargable battery?


*NO* battery "likes" to be fully discharged!


Not true. NiCds and NiMH batteries can be fully discharged, but not below 0V on any cell. A multi-cell NiCd battery may reverse charge a weak cell which *will* kill it. NiCds should be stored discharged (but self-discharge is good too).

OTOH, lead-acid batteries must never be fully discharged. Deep discharging them tends to warp the plates causing shorts. "Marine" batteries have thicker plates (thus lower power-density and higher internal resistance) and are less susceptible to plate warping.


That being said, the NiCd cells have a "memory" problem, and the only way to "reset" that is to do an almost complete discharge and then charge; sometimes this is needed moer than once for recovery.
So, this regimen to "reset" their memory theoretically reduces their lifetime - but without the "reset" they are useless anyway, making the theory un-proveable and moot.


The "memory" problem isn't. It's much legend about a totally different issue (one that has been pretty much non-existent for 20 years).


Other uses that can shorten cell lifetime is heavy discharge and heavy, un-controlled charging.


Over-charging and reverse charge during discharge are by far the most common cause of early failure of NiCds.


Roughly, a cell should not be discharged to less than 80 percent of rating, and the discharge rate should not be greater than C/2 or only "bursts" of C *if* the chemistry supports that.


Not less than 80% of rating? Nonsense. Lead-acids shouldn't be discharged below 20%, perhaps. NiCds can be run to down to zero as long as the cells don't reverse polarity. 

Not a pack, just an individual cell. The *proper* discharge
level - the level at which the cells should be considered
completely discharged - is about .9v per cell.  With a single
cell there is no risk of cell reversal, but with a pack,
discharge should be limited to that .9v per cell level.

Lead-acid 12V wet cell batteries should never be discharged
below 10.5 volts.

Ed


You'd better talk to model airplane nuts and electric drill manufacturers about your C/2 or C "rule".

.

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