The 200mAh basically means that, if you draw 200mA then it will last 1 hour.
You need to know the total current draw. I would suggest placing an ammeter in between the battery and the power input (in series in the positive line) and measure the actual current requirements.
Then you can calculate how long 1 battery should last.
I don't know what made you think that?
Not knowing the spec of the LEDs doesn't help but I make it probably closer to 320mA rather than 400mA, but that is still a lot for a whole day.
That should say:-
Make sure you use a low-impedance cow - bull
Is it an outdoor showing by any chance? Maybe a solar panel?
also using say AA's or even some d batterys will last a whole lot longer, maybe use an ldo regulator to keep the battery voltage as close to 5v as you can, or go into the 3.3v range and draw less, while still being enough for the leds and wasting less power across the resistor
fubbi:
I am "in the field" and the little pocketmeter i brought can't measure A
I would -love- to see a picture of this meter; unless this thing is about 30-40 years old, I can't believe that it would only measure resistance and voltage, but not current (as if you can do those two, you can kinda get the third almost "free"). I mean, I can go down to Harbor Freight and purchase a full multimeter (Cen-Tech piece-o-junk that it is, good enough for most purposes, though) with all functions, including transistor and diode check features for $1.99 USD with a coupon; so I would really like to see what someone sold you. You probably got ripped off, if it is as you describe, unfortunately.
4 LEDs in series will drop approximately 6-8 Volts (depending on exactly which LEDs you're using).
Add a resistor to limit it to 20ma. (If your LEDs use 6.8 V, the remainder is 2.2V that the resistor has to drop. 2.2V/0.02A = 110 ohms.)
Make 5 strings like this for a total of 20 LEDs.
If you want your battery to last, you need a switched mode regulator circuit.
Instead of the, say, 25% efficiency of an LDO, you'd have nearer 80% or more with a SMPS.
You could easily use a car cigarette lighter -> USB adaptor. That will give you a good 5v with little power wastage. Most of the chips they use handle between 7.5v and around 70v as an input.
4 LEDs in series will drop approximately 6-8 Volts (depending on exactly which LEDs you're using).
Add a resistor to limit it to 20ma. (If your LEDs use 6.8 V, the remainder is 2.2V that the resistor has to drop. 2.2V/0.02A = 110 ohms.)
Make 5 strings like this for a total of 20 LEDs.
Total current draw is 5 *20ma = 100ma.
sounds good, I have already built the circuit with 4 transistors so I need 5 led on each... Also I have soldered 220? resistors to all my leds already...
I am off to the electronics store now, any last second advice? lead battery?
yey! thread out of control the day before my installation at the gallery. thats not stressful at all... anyway I ended up going for a Led battery with 12aH, that should last for the day