<html><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:10pt"><div><span>Hi Chip,</span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><span>Paralleling
batteries is a tricky business. Batteries never have exactly the same
voltage. The highest voltage battery will discharge into the lower
voltage cell. If a battery in parallel experiences a shorted cell, that
battery will rapidly discharge the other batteries. In commercial
installations, large batteries are only connected in parallel with
protection (diode or more complex current sharing) to prevent power loss
and/or fires.<br></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><span>I
would suggest connecting the two Lithium batteries in series and then
using a buck converter to regulate down to what you need for your
project. On-semi (was Motorola) and Texas Instruments both offer PTH
controllers, but you have to add the other ingredients (output inductor
and cap, input cap, catch diode, etc.). It is also highly recommended
that you lay these components out on a PCB instead of flywires.<br></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><span>The
good news is that you can buy pre-made modules using TI's (formerly
National Semiconductor's Simple Switchers) LM259x controller on Ebay for
as little as $5 in single quantity or less if you buy 5 or 10 in a
lot. They are small, simple to use and have potentiometers built in to
adjust the output voltage. They are advertised as having 90+ percent
efficiency but that figure is dependent on the load. They are very
handy for small projects and will get you running in less than five
minutes.</span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><br><span></span></div><div style="color: rgb(0, 0, 0); font-size: 13.3333px; font-family: HelveticaNeue,Helvetica Neue,Helvetica,Arial,Lucida Grande,sans-serif; background-color: transparent; font-style: normal;"><span>Good luck,</span></div><span>Kevin Schilf</span><span><br>Digital Telesis, Inc.</span></div></body></html>