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Date: Wed, 16 Feb 2005 17:38:11 -0500
From: Ernest Christley <echristl@cisco.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Battery voltage (was: Racetech RV6A Forced Landing)
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Alex Madsen wrote:

> It seems to me people should be using deep cycle marine batteries for 
> there aircraft. A deep cycle marine battery will give much better and 
> longer performance with a dead alternator.
>
>  
>
I don't think that's true, Alex, unless by 'dead alternator' you're 
referring to the guy with getthereitis who quick charges a low battery 
to get juice to get to a destination when he has a known alternator problem.

When a battery isn't charged, the acid eats the lead and the resultants 
gunk drops to the bottom of the battery where it can never be 
reconverted back to a usable state through the charging process.  The 
deep cycle batteries avoid this problem by not exposing all of the lead 
to the acid.  Some still gets eaten away when the battery is completely 
discharged, but the lead plate is thick enough not to care.  It doesn't 
hold any more electrons is store, and since there is less contact area 
between the plates and acid, it offers more resistance when the 
terminals are shorted (which is what happens when you throw the starter 
switch).

They are more robust (as far as charging regime is concerned), but carry 
a weight penalty.  A much better solution is a well maintained 
electrical system, and a trickle charger at the hangar.