I have nothing against a device like the Battery Minder, but lets put a few things in perspective.  A battery is an expendable, not an investment.  If you fly IFR, it needs to be in top shape so it can get you out of IMC and on the ground in a reasonable amount of time in the event of an alternator failure.  Sure, you can lower your flying cost by squeezing another year or two out of a battery, but what are the savings and what is the risk?

The safe thing to do is to change the battery every year -- 2 if you are feeling brave.  Trying to extend the life of a battery is fool hardy.  In the worst case, all that a Battery Minder will do for you is to increase the value if your estate by $5.

Hamid,

 

You must have missed much of the discussion about batteries that have occurred over the last few months.  The objective is to keep the battery at its' rating over whatever time period one chooses to use it - even as short a time as the first year of use.

 

While it may seem that these devices are used to raise the dead, their better use is for maintenance. 

 

We have learned that there are many SLA batteries (including Glass Mat), definite brand preferences (sometimes by emotion or reputation rather than test and use) and definite differences between brands and purposes.  Some individuals are interested only in cold cranking power, some in holding up heavy emergency power loads for a shorter time period, and some in lesser starting loads, but longer delivery times for smaller loads (essential bus, backup power).  Have no doubt that there are different implementations to satisfy such different requirements.

 

I agree, the batteries in my airplane (main/essential and EI backup) are not expendable when I am flying. 

 

For certain batteries, Battery Minder and/or Battery Tender can be used to maintain them to deliver the rated power for each and every flight the batteries are used, whether it is for 1 year, 4 years or even many years after retired from their aviation service.  A battery's service life can be limited by dormancy, repeated excessive discharges and charge cycles - not necessarily just time in use.  A battery maintainer can improve the odds your battery will not fail you halfway thru your next flight.  This is the safe thing to do. 

 

A battery depleted by the master switch left on may be recoverable because the master relay couldn't stay held in to a complete discharge.  Leaving the essential bus switch on for a week will completely kill a battery because it will suck every electron out (to keep the gear down and locked lights on) and never let it bounce up even a bit.  One battery may be restored, the other may spend the rest of its' recovered life (if any) starting my tractor - top speed is 8 mph close to the ground in rain, sleet, fog or sunshine.