urgent - battery tester

[egasimus]

I need to make myself a simple battery tester. I have red 3mm leds, 1n4007s, 1n5819s, and resistors. I want the leds to light only if the battery voltage is above 8V.

[slacker]

LEDs drop about 1.5 - 2 volts across them, diodes drop about 0.6 - 1 volt, so stick about 4 LEDs in series with say a 100 Ohm resistor and connect them to a fresh battery. Measure the voltage across the LEDs, adjust it so it's somewhere between  7.5 volts and 8 volts, by adding LEDs or diodes in series.
It's a bit rubbish but that will light the LEDs with a fresh battery and one that's somewhere round 8 volts might light them dimly, somewhere below 8 volts they won't light up.

[sundgist]

I have red 3mm leds, 1n4047s, 1n5891s, and resistors.

Limited to using these?  
#edit# (just noticed the word urgent in the title!)

As suggested above or stack up 8 or so diodes in series before the led and resistor or get a 6v / 7v (can't remember standard values) zener diode instead of the diodes.

[Gurner]

You're limited to a sort of woolly battery tester if you're constrained to only using your listed components - you really need to bring something like a zener and a comparator into play if you want an led on/off for above/below 8V type scenario.

[Philippe]

Wouldn't it be far easier just to use your DVM & pinpoint any DC voltages >8 volts?

[egasimus]

damn, two typos - those were 4007 and 5819s.

I'm having a hard time balancing current draw and voltage drop, since I'd prefer to have either 2 or 3 LEDs, everything else oughtta be resistors and diodes.
Also, 3 LEDs is series with a 4007 and a 5.6k light happily, while Falstad's sim says there's only nanoamps of current through them (and when I try to measure current with my multimeter, they don't light at all).

[Gurner]

If you want to go *really* low parts count - just use your tongue ......8V stings!  

[egasimus]

What I just came up with on the breadboard: a resistor, two leds, and a 5.6v zener, all in series. Seems to work nicely.