In SX Microcontrollers, SX/B Compiler and SX-Key Tool, william wrote:

Sorry Ron,

There was a slight mistake to my advice.

You may need a P-Type mosfet instead of a N-Type mosfet like the IRL510, because once the the divider is blocked from accessing ground by the transistor, 
it would no longer "divide" voltage, the middle point would rise to the voltage of the battery.

When that happens, current would start to leak into the 2 IO pins of the SX.  Not much harm done but it defeats the purpose of the mosfet/transistor.

It may be better to just use a higher resistance value for the divider like 50k and 100k for the ADC without any transistors.

In this setup, the divider would continuously "waste" almost 50 micro amps, which is not bad considering that the LP2950 regulator also waste about the same amount continuously.  ( this is much much better than a 7805 which leaks 3mA ).

This is the compromise you have to make to allow monitoring of the battery.

Good Luck.

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