GeoLane at PTD dot NET wrote:

Put 2 silicon diodes in series with the battery to drop 1.4 volts,
giving you the ideal 14.6.

5 amp 25 volt should do.

I did that today. I had the original diode and a 10A diode. It
didn't change it even 0.5 V

Your test probes should be on the battery terminals
themselves. Is that how you are taking your readings?
Placing the test probes on the clips attached to the
battery can sometimes provide false readings.

--Winston