Another solution is to insert a step up switching type voltage regulator
between the radio and the battery. Need only run at a few KHz for
keeping the noise down with larger L and C. Let it produce 13.8 or 14
volts while the battery falls from fully charged at 14.2 (while
charging) down to 10.5, but feed the radio 13.8 the whole time.
Efficiency can be very good. Then the internal regulators in the radio
can function properly and the PA can supply full power, but when the
battery passes 10.5 volts its probably dropping a volt a minute with
something like a Corsair II loading it. At least that's the way
batteries I've checked with something like a head light load and a strip
chart recorder of terminal voltage. When it passes that bend around 11
volts its ALL done.
73, Jerry, K0CQ
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