A battery question for the $50 robot

[TheDarkLord]

Hi, I previously posted this in another thread, but became skeptical when I saw that it was from 2009, and so I'm posting again, sorry for that.

I'm currently building the $50 robot and I have some questions regarding the battery.
I couldn't get hold of a battery pack, so would it be fine if I connected 5 AA batteries in series and pretended it was a battery pack? Also, could I treat it as a normal battery pack in terms of charging and following the rest of Admin's tutorial? And finally, how can I measure the amperage (mAh) after 'putting together' this battery pack? I have a multimeter but the max current is 200 mA..

Any help would be greatly appreciated.
Thanks in advance,
Vignesh R.

[corrado33]

A battery pack is simply that, a bunch of batteries in series with a nice connector on the end.   

So yes, you could connect 5 batteries in series to make a "battery pack".

Could you charge it?  It depends, what type of batteries will you be using?  If you use rechargeable ones, and they are all the same size and have the same mAh rating, then yes, you can charge them.  If they are normal non-rechargeable batteries, no, you can't recharge them.

The mAh rating of batteries in series is simply the mAh rating of a single battery in that series.  So if you have 5 2500mAh double A size batteries in series to make a battery pack that provides 6V, it will have a rating of 2500mAh.  If you had two of those battery packs, and you connected them in parallel, it'd provide 6V with 5000mAh.

I'm pretty sure all batteries have their rating on the packaging SOMEWHERE, you just have to look for it. 

[TheDarkLord]

Thank you, I really appreciate the quick reply.

I can buy either 5 1.2V NiCD batteries or NiMH batteries. Based on experience, which would you recommend for longer life (as in number of times they can be recharged)?

[TheDarkLord]

Oh, and one more question (sorry, but this is my first robot haha)

I have a standard power adapter black box thingy which outputs 6V at 300mA. I could use this to charge my makeshift "battery pack" yes? Or do I have to buy a real charger? Also how long would it take to charge assuming I buy 5 1.2V NiMH batteries of 2100 mAh each?

Thank you so much!

[corrado33]

I've never used NiCd batteries, so I do not have any first hand experience however...

The differences between NiMH and NiCd are quite easy to find online.

NiCds are generally used in high drain applications where you need a lot of amperage out of your battery pack.  I'm paraphrasing from a quick google search I just did now...

NiCds generally hold less power than a similarly sized NiMH.  However, NiMHs self discharge quickly.  They'll drain themselves if you don't use them.  Generally you'd want to charge them right before you use them, or the night before.  They DO have new NiMH batteries out that improve on this.  

NiCds sometimes have a problem called the Memory Effect, which improper charging can cause.  So, you have to be aware of that.  Google it to find out more.

From what I'm reading online, NiCds can be charged and recharged more (but you have to worry about the memory affect).  With that said, I bought NiMH batteries... probably close to 4 or 5 years ago and they're still going strong (although my charger doesn't seem to like to know when they are charged anymore, so I have to watch them closely).  

In the end, I'd go with a NiMH unless you NEED a ton of current, which you probably don't unless you're planning on hooking up a ton of servos and they'll all be moving at the same time.

I can't help you with your battery charging black box power adapter.  I'd suggest buying a real charger if you want the best life out of your batteries.  Good chargers are relatively expensive though.  Considering the voltage of a NiMH 6V battery pack would be closer to 7V when fully charged, I'm not sure how well that one you mentioned would work charging it.  (Remember, a battery's voltage drops as it gets used.  So it'll start out at 7V or so, then drop to... oh I dunno 4.5V or so when discharged.  This is why we have voltage regulators).  Then again, like I said before, I have no idea if it would work or not.