When to recharge

Im currently using AAA alkaline batteries. The 3pi reports a voltage of 5822 mV. I have just fully charged 4 AAA NiMH (850 mAh) batteries, and these display 5520 mV. My question is , what level should i recharge these at? I saw 1 post that suggested recharge at 4800 mV is that safe? What do you think?


To get a precise answer, you need to know the discharge curve of your battery. Yes, something close would be to recharge, if the voltage falls below around 4.8 V.

- Ryan

Maybe I’m doing something wrong, but I don’t recharge NiMH batteries until they die – the 3pi shuts off on it own. I wouldn’t program with them lower than ~4.8V though.

NiMH batteries don’t have permanent memory issues, but they can have their capacity temporarily limited by not fully discharging several times. At least, that is what I’ve read.

Darth Maker’s post makes a really good point: it generally doesn’t matter to run your batteries out until the 3pi shuts off, except if you are trying to program it, in which case a power failure could render the AVR unusable. 4.8V is a very conservative threshold for that programming consideration. You’ll also get a fairly different reading depending on the load, so if you get even 4.7V without the motors running, the batteries probably are getting on the low side. Fully discharged is probably when they get under 4.0V, so you should definitely avoid programming under that voltage. The 3pi probably won’t cut out until around 3.0V, but under 4V, the voltage will start dropping really fast.

- Ryan

Thankyou very helpful