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Rechargeable battery for NXT 
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Joined: Thu Oct 16, 2008 10:54 am
Posts: 2
Post Rechargeable battery for NXT
Does anyone know if the rechargeable battery for the NXT should be fully discharged before re-charging it? Also, the documentation that comes with the NXT educational sets says that the battery should not be installed in the NXT the first time it is charged? Will this make a difference in the lifetime of the battery?

Thu Oct 16, 2008 11:00 am
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Joined: Sat Mar 01, 2008 12:52 pm
Posts: 1030
Post Re: Rechargeable battery for NXT
The accu's are LiMH, so they don't have any memory effect (like NiCd) and so they can be charged and discharched completely or partly, just as you need. I didn't find any information on lifetime dependencies to this, I guess you don't have to worry about this.

HaWe aka Ford
#define S sqrt(t+2*i*i)<2
#define F(a,b) for(a=0;a<b;++a)
float x,y,r,i,s,j,t,n;task main(){F(y,64){F(x,99){r=i=t=0;s=x/33-2;j=y/32-1;F(n,50&S){t=r*r-i*i;i=2*r*i+j;r=t+s;}if(S){PutPixel(x,y);}}}while(1)}

Thu Oct 16, 2008 11:31 am

Joined: Fri Sep 19, 2008 1:22 am
Posts: 200
Post Re: Rechargeable battery for NXT
LiMH batteries do not have the same kind of "memory" problems that NiCad batteries have. However, they still only work for a finite (but large) number of charge/discharge cycles. This means that frequent charging will not reduce the usable capacity of the battery but it may shorten the overall life of the battery.

Jeff McBride
Benson Robotics Club

Thu Oct 16, 2008 11:39 am
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Joined: Wed Jan 31, 2007 3:39 am
Posts: 299
Location: San Diego, California. USA
Post Re: Rechargeable battery for NXT
Hi NVaTeacher,

I have been using the rechargeable battery ever since I got my first NXT over a year ago and it is still working fine. I use if for a couple of hours and rarely discharge the whole battery, then charge it overnight, and it still works. I would make sure the battery is fully charged before you use it for the first time just to be safe, they come shipped only partially charged.

Hope this helps B-)

Mmmm Legos B-)

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Thu Oct 16, 2008 12:51 pm
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Joined: Fri Feb 09, 2007 9:21 am
Posts: 616
Post Re: Rechargeable battery for NXT
I have several batteries that no longer hold a charge. I strongly suspect that it is not good to leave the battery on permanent charge for days (or weeks) at a time.

I've been told that this should not be a problem, but my real-life experience suggests that it is.

Thu Oct 16, 2008 3:10 pm
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Joined: Fri Nov 09, 2007 4:51 am
Posts: 121
Location: Hungary, Europe
Post Re: Rechargeable battery for NXT
Batteries do not like if they are fully discharged and kept in that state for a longer period of time (weeks).

General NiMH bears ~1000 charge cycle, some manufacturers claim ~3000, probably based on the assumption that no one will claim after a few years of usage.

Charge cycles refer to more or less full discharge and charge; partial discharging and charging uses less of the lifetime (just think of segway or toyota hybrides where every braking charges the battery).

Fri Oct 17, 2008 12:16 pm
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Joined: Sat Sep 20, 2008 12:16 pm
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Location: Curently fighting aliens on P3X-828
Post Re: Rechargeable battery for NXT
NiMHs do have an issue with not holding their charge very long, and also cannot be let holding a charge for more the a few weeks. However, they do not have issues with cell memory.
edit: Don't forget that Lexus uses the same tech on the RX 400h, since Toyota owns Lexus.

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Tue Oct 21, 2008 2:58 pm
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