Decided to put my $$ where my mouth was and ordered the Battery Tender Plus (1.25A charging rate).  This retails for $59 but I found an online retailer selling brand new units through a well known auction house for $39.95 plus shipping.

At nearly 3 lbs, I was a little surprised by the heftyness of the unit but it is a sturdy powder coated aluminum chassis.  Physical size is 4.88 x 3.25 x 2.88" and comes with 2 quick disconnect leads.



Speaking about leads, the Battery Tender Plus (as well as the Jr model) has a "spark proof" feature where there is ZERO output current until the unit can detect a viable battery has been connected.  Try to touch the leads together with no load on the system and --- nothing!  One set of leads is the familiar spring clamp style and the other set is terminated with eyelets.  The eyelets are intended to be permanently attached to an installed battery as a pigtail setup.  Simply remove the dust cap from the quick disconnect fitting and attach the Battery Tender Plus.

I use a 12v 7.5Ah gell cell for my field box.  Keeping this optimumly charged at any given time is a challenge with standard or automatic trickle chargers.  These smaller lead acid, absorbed glass matt or gel batteries are easily damaged by overcharging.

The Battery Tender Plus utilizes a 4 stage microprocessor controlled charge cycle.

Stage 1 = Qualifying evaluation (insures safety by properly verifying battery status prior to charging).  Accidentally get the leads reversed?  No problem.  Remmember you need a properly connected battery hooked up before the output circuit is energized.

Stage 2 = Bulk charge where the BT+ raises the battery voltage to 14.4 Vdc.

Stage 3 = Absorbtion charge where the BT+ holds the voltage at 14.4 Vdc and forces current to fully charge the battery.  This could take anywhere from a few hours to a few days to complete.  There is a built in 72 hour timer which will protect a marginal battery from over charging.

Stage 4 - The unit switches to a float charge where it maintains a fully charged battery at 13.2 Vdc.  This is NOT a trickle charge where a constant current is put into the battery.

I took my gel cell which has been sitting unused for the past 3 months.  The Battery Tender Plus displayed a steady red LED meaning a battery was properly detected.  The green LED was flashing which meant the unit determined my gel cell still had 80% of its capacity and "could" be returned to service.  After 3 additional hours on the charger the green LED stopped flashing and showed a steady green.  This meant the battery had completed it's absorbtion charge and now was in it's float charge mode.  It can be left in this mode continuously but Deltran suggests regular inspection to guard against any malfunctions.

The unit has a 10 year warranty.

I've had to replace these motorcycle batteries every couple or three years becaus they are difficult to maintain during the long winter months of non-use (or heavy use during the flying season).  With the Battery Tender Plus, I simply plug it in and leave it until ready to fly.  Then I know it will be available to deliver peak performance.

Hey Steve,
 THAT is a great idea! I sell these things at the dealership and didn't even think of using it for the flight box. I stock the Junior for $31.99 and can ship them to anyone interested for $6.00 ground in the U.S.

I went the other route and got 10 C cell nicads.  About the same price.  Hold charge a loooong time and only need a quick overnighter(or a $5 trickle charger) to bring back up to full charge.