Let's Make Robots!

what battery to choose?

please advise me upon what battery to choose,

my requirments are,


Iout= upto 700mA

the battery must be rechargeable, light weight. the requirments may even be met with series/parallel combinations of the batteries.

NOTE: I might use regulated outputs from solar panels for the purpose of charging this battery, so consider that too.


Thanks in advance.

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If you need something light you might consider using a one of these voltage boosters and two rechargeable NiMH AA batteries in series (or a different battery), you should be able to get nearly 700mA output from the voltage booster.

battery charging can be a tricky thing that requires a fair amount of trial and error.   matching the right charge method / circuit to the specific battery in use.

currently I'm using a 9v panel rated for 100ma, to charge 5xAA nimh (2300mAh), with occasional sun exposure it after year or more, the device is still going.  the bot is little compass in my truck, used almost every day and night.   I havent changed the batteries yet.

for the panels I was using, goto www.parallax.com and type in solar panel in the search box - you'll see the square 9v panels along with smaller 6v panels.

5 of the above mentioned batteries should provide 6v and in the neighborhood of 700 to 900 mAh. I am not so sure on light weight, but, they are easiest to recharge. Wikipedia says typical mass for AAA NiMH is 14-15g. Five should then have a mass of about 75g + about 15g for a 6 cell AAA battery holder. You could then insert a dummy battery in one of the locations to maintain your 6v.

Thanks for the info, but will it be ok to recharge these battries using solar panels?

and will the "memory effect" thing be a problem?

Also how much would be the average cost of each individual batery?

Check out the MAX712 chip. An excellent all-in-one charger chip that will power the load while charging the battery. Highly recommended.

I forgot Ezekiel made a nice 712/713 writeup that reduces the datasheet information into easily digestable chunks. It was too late for me but I think it's good for the first timer.

with solar cells as long as you do not exceed 10% of their rated output current. Battery prices vary. Do a search and find a local shop that carries what you are after. Remember never mix and match cells. If you have 5 cells and one goes bad, do not replace the single cell and think things will be business as usual.