The Dave Lawton 9XA

Source: http://quanthomme.free.fr/qhsuite/2011News/imagenews11/MeyerReplicatAnglais29pages.pdf

The Dave Lawton 9XA is a versatile pulse and gate generator with variable duty cycle on both 555 timers.

One design note that exists here, is that Pin 3 Output of timer 1 is used to provide Vcc power to Pin 4 on Timer 2. This means an inherent latency is always introduced by the 1st RC charge cycle to power up the 2nd timer. This would cause a partial leading pulse. Other than that issue, it's a pretty solid circuit.

Using a BUZ350 mosfetto pull down the B+ 12V through the cell and negative choke.