Hints for Many NiMh In Series

I use 11 NiMh in series to create a 15V battery pack. I use this to power a radio transmitter, which intermittently draws 2A. I observe basic NiMh care (I use a Maha C801 smart charger and I run them through a conditioning cycle after 20-30 charge cycles). Given my unusual 11-in-series configuration is there anything in particular I ought to be doing in order to maximize cell life?

I can't get the right voltage out of Li-Ion, so "switch to Li-Ion" isn't an option. ;-)

You may want to check the internal resistance and match the cells. Usually unbalance is more severe when there are more cells in series, so its hard to notice if the voltage drop is near the minimum voltage of one cell in that series.
Other than that, you may want to use lithium chemistry with a voltage regulator, that will require less cells and it's easier to balance them with a hobby charger in a single charge.

I don't see why you can't switch to LiIon.

If 11*1.2V=13.2V works fine I don't see why 4*3.7V=14.8V would not work if the requirement is 15V. Also 4 18650's will give you way better run time than 11 AA's.

In most cases, 4 18650s would be an alternative. However, you're looking at nominal voltages. When they come off the charger, 4 of them actually produce slightly more than 15V. I'm dealing with a "smart" device which detects the too-high voltage and shuts down. Since my use-case is hiking 10 miles with a radio to the top of a mountain to talk to people from around the world, auto-shutdown is... anti-climatic.

I could use 4 18650s with a voltage regulator, but I'd have to fashion some sort of enclosure. (It has to stand up to a 20-mile round trip, crammed into a backpack.) I can certainly handle the electronic side of that, but I'm not much good at fabricating enclosures. If I could wave a magic wand, I'd buy a 15V voltage regulator in the form factor of an AA battery. Then I could load my 18650s and the voltage regulator into an existing AA enclosure and get 15V out.

You could use a DC to DC converter. However with current that high it will be bigger than a AA battery but not a lot bigger, 2.5"x2.5"x .5" approximately. More like the size of 3 AA's.

http://www.xppower.com/Portals/0/pdfs/SF_ICH-IFH.pdf

kleinfelter said:

[...] I could use 4 18650s with a voltage regulator, but I'd have to fashion some sort of enclosure [...]

Click to expand...

They're called "powerbanks" and there are numerous available that output 15V or 16V, some with easily replaceable (18650) cells.

What voltage range does your device require, and what capacity do you need?