ON-off circuit almost works

[gregfox151@gmail.com]

Hello all, I would love some help on a problem I uncounted. The circuit attached is a on – off  circuit with low battery cut off and reverse voltage protection. It works just great, that is, almost up to my design voltage of 16.5V.
The circuit is designed to allow a rechargeable 14.8V battery (16.8V fully charged) to power a circuit. The circuit only draws 1 or 2 uA and can be powered (almost) forever. If the voltage gets too low the battery could get damaged, thus the low battery turn off, set by Q1,R4,R5 and d3

If turned on at below 13.3 volts, it will stay on up to the input of 16.5 volts. However if the voltage is set at 16.5 volts LED D4 will only flash on and then go out.  In other words it will not stay on.
The 4013 is rated up to 18V, and I turned down R36 to minimum (towards GND) in an attempt to eliminate it from the circuit. I also bypassed Q2 to eliminate it.
Can anyone explain why it will only turn on up to 13.5V?
Thanks!
Forgot the 4013 is a MC14013BDTR2G

[dannyf]

Just a suggestion for the reverse polarity circuit: check out an application note from IRF. It can be done with either n- or p-channel mosfets alone, no resistors or zeners. And it is quite efficient - once on, it has only Rds in the circuit (less of a concern here).

As for the rest of your circuit, they seem to be too complicated for what you are trying to do. You should be able to get it done with comparators or a mcu.

[gregfox151@gmail.com]

Thanks I'll take a look. The circuit is really quite simple and works really well except for that pesky 16V.