The best batteries in the world...
... are NiMH AA cells.
It's quite simple:
- They store a lot of energy. Decent quality cells are rated at 2.4Ah nowadays. I remember a few years back, when a rechargeable AA cell could only store 500mAh, and a C cell was 2Ah. And we had to walk fifty miles in the snow to... oh, wait.
- They're rechargeable. This is a no-brainer. I go through far too many batteries to be buying new ones regularly.
- They're cheap. The price of quality rechargeable AA cells has remained roughly constant for the last 15 years - $5/cell. That used to be a lot of money for me 15 years ago - but now, I have dozens of the things.
- You can buy quality fast chargers off the shelf. My current favourite is a one hour charger that takes about 15 minutes most of the time. The cells get hot, sure, but it's fast! Supermarkets stock chargers now. This is no longer a niche technology.
- They're robust. During charge, during discharge, and physically, these cells have held up remarkably well. My charger is rather cruel to cells - making them too hot to hold, sometimes - but no cells have died yet. I've powered halogen lamps off these cells - at a 1.5C discharge rate, also making them rather hot - but no deaths. The worst physical environment that I can think of that I put these cells in is my GPS mounted on my mountain bike, where it gets wet, salty, dirty, and endures a hell of a lot of vibration, not to mention collisions and crashes. I've had one cell die in there after about a year.
- You can build a charger with some fencing wire and a couple of blobs of blu-tac. Well, almost. But a simple current-limited charger will work admirably, and your cells won't explode spectacularly when you overcharge them, like lithium ion ("venting with flame").
- They survive plenty of charge cycles. None of this "hundred charges and you're done" crap. They just keep coming back for more. I have three-year-old cells that still have most of their original capacity.
They really do hold a special place in my geek heart.
At peak charge a typical
At peak charge a typical cylindrical NiMH cell can be as high as 1.45(n)V or thereabouts. They'll soon enough settle down to a sub-1.40V value if left out of the charger or ran for a moment in any device using more than a tiny mA current. Some prismatic cells might reach slightly over 1.50V but they too tend to peak closer to 1.45V
As for the other end, generally we consider them drained at 0.8V though whether that's the figure to use can have a bit to do with how you're powering your (LED bike light(?), etc, whether there were a regulation stage between the battery pack and device or just a current limiter like a series resistor, at which point you'd consider the device function to be falling below a minimum acceptible threshold.
NiZn
I believe the 1.7 volt rechargeable batteries you're thinking of are NiZn (nickle zinc), not NiMH. That's a technology that's still "getting here", so to speak, so my vote goes to NiMH AA cells also.
Ian.
Sub-C model car packs..
SubC RC car packs are good value too e.g. http://vapextech.co.uk/acatalog/High_Power_Model_Control_Batteries.html - and I'm sure you can get them cheaper elsewhere as well (at least you can with practically everything else in the UK - even if it's made here)!
output voltage of NiMH
Most of my NiMH batteries have output voltage of about 1.3 to 1.4volts, i been reading on a website about Garmin 60cxs GPS that NiMH cells can output upto 1.7volts. And this high output voltage can causes problems for some devices. Anyone know the voltage output ranges of NiMH cells?