I have a project where small size is very important. I have a tiny motor which needs 5 vdc, has an inrush current of about .2a and a continuous current of about .1a. It only needs to run three times for about one minute or so the capacity is not a big issue. The battery does not need to be rechargeable, I will not use it a lot.
I'm sure three aaa batteries would work, but I'd like to go smaller. Unfortunately watch batteries don't seem to come with spec sheets which tell me the max current they can supply.
I would appreciate any input.
Thanks in advance.
You could use a single 1.2-1.5V cell of several types, and a very small boost converter to produce 5V.
How long do you need the battery to last ?
A single cell in a clock battery can have a high stall current but last for a year.
I don't need the battery to last very long at all. Three minutes total usuage, and can be charged/bought for the single use event.
The boost converter looks interesting, but seems to defy the purpose of the small battery.
seems to defy the purpose of the small battery.
In what way?
You might want to investigate some of the coin cells - go to Digikey.com or Mouser.com for example and look at the specs for something like the CR2032 - 3v @ 240mah. Two of them in a holder would give you 6v which would be just right for one diode drop in series so you can't put the batteries in backwards and blow things 
Those are pretty small, available lots of places and not very expensive.
HERE is a data sheet for one and the next size up as well.
I don't think they can/should power a 100-200mA motor.
The internal resistance, according to several datasheets, is ~10-40ohm.
No harm in trying though.
Leo..
I would suggest LR44 batteries (aka AG-13) which is small enough and perfectly powers the motor of those Hexbugs.
datasheet http://data.energizer.com/PDFs/A76Z.pdf
Internal resistance of an LR44 is worse than a CR2032.
Datasheet states a test discharge of <=200uA.
500 times less than what is required by OP.
Leo..
DeucesAx:
I don't need the battery to last very long at all. Three minutes total usuage, and can be charged/bought for the single use event.
Sounds like you need a thermal battery.
As used in stinger missiles. :o
Perhaps a coin cell in parallel with a supercap would do .
Possibly a miniature lipo.
They can be smaller than a postage stamp.
gpsmikey:
You might want to investigate some of the coin cells - go to Digikey.com or Mouser.com for example and look at the specs for something like the CR2032 - 3v @ 240mah. Two of them in a holder would give you 6v which would be just right for one diode drop in series so you can't put the batteries in backwards and blow things
Those are pretty small, available lots of places and not very expensive.HERE is a data sheet for one and the next size up as well.
Hopeless. Look at the graphs in that link! CR2032 will get you 2mA before fading. These are calculator
batteries.
Even LR44's are going to struggle I think (alkaline button cells, 3 in series gives 4.5V)
I would recommend using 3.7V is at all possible, LiPo won't have any trouble with 0.2A
Wawa:
Internal resistance of an LR44 is worse than a CR2032.
Datasheet states a test discharge of <=200uA.
500 times less than what is required by OP.
Leo..
1 to 5 ohms internal resistance is what the datasheet said, ie far better than CR2032.
Yep, missed that.
Must use four of them in series then to counteract the IR of 4-20ohm.
Three could be enough for the application.
Leo..
any idea how much power does a hexbug motor use?
they seem to run pretty fine with lr44s but I guess they might be low power ones than what OP suggested.
MarkT:
1 to 5 ohms internal resistance is what the datasheet said, ie far better than CR2032.
Did you look at a specific brand? I goggled but did not find any that showed internal resistances that low.
I've got a similar project and am going with the power booster. The module is tiny - smaller than a coin and can boost .8V upto 5V to run a small vibration motor..