>                     I have a circuit using a 16f874 , with a total power
> consumption of 500 mA, the circuit have some 7805 voltage regulators in
> parallel that reduce the voltage from 12 V to 5 V. I'd like to add a
> backup rechargable battery circuit, that gives me 6 hours of backup
> when the main power goes off. If somebody knows about some reliable and
> cheap solution i'd appreciate it. Thanks in advance.

I would replace the linear regulator with a buck regulator so that you are
no longer wasting 60% of the power.  Even if not, you are only asking for
3AH from the battery.  Sounds like a good application for a lead-acid gell
cell.


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