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As an update on the Battery Xtender, I thought I’d post some results from testing with a multimeter.

I took four unused Energizer AA batteries, three expiring in 2009 and one unmarked (with the “Test” strip on it), and put them in a Garmin GPS III Plus. The GPS was turned on and left on until it turned off due to lack of battery power (more than a day), then turned on and left to drain to empty.

All four were marked (1-4) and tested with a digital multimeter before and after being drained by the GPS. As expected, before being drained the older battery tested slightly lower (1.576V) than the other three, which showed identical voltage (1.592V). After the GPS was done with them, again the older AA tested lower (1.158V) than the other three (1.195V, 1.171V, and 1.206V).

They were then put into the recharger in order, and charged until all four LEDs showed green on the Battery Xtender.

The voltage was then retested, with curious results. The older battery had been charged to 1.414V while the other three were 1.343V, 1.338V, and 1.393V. After scratching my head a bit, I guessed that the effectiveness of the charger on each battery might have something to do with the position in the recharger unit, and so returned the batteries to the recharger for a second round of charging in a different order. The two previously in the middle (at positions 2 and 3) would now go to the end positions (1 and 4), with the previous outer two now in the middle.

The results this time were better. The four now read (in order of their new positions in the recharger): 1.431V, 1.411V, 1.391V, and 1.338V for batteries marked 2, 4, 1, and 3 respectively.

	Battery 1	Battery 2	Battery 3	Battery 4
Listed Voltage	1.5V	1.5V	1.5V	1.5V
Start	1.576V	1.592V	1.592V	1.592V
After drain	1.158V	1.195V	1.171V	1.206V
First charge	1.414V	1.343V	1.338V	1.393V
Second charge	1.391V	1.431V	1.418V	1.411V
Update: Another charge attempt, this time in order 3, 4, 1, 2. Looks like the other positions are the best, topping out around 1.43V
Third charge	1.393V	1.429V	1.428V	1.372V

It seems that charging in the first and maybe last positions of the Xtender results in the best charge. However, I’ll see what effect repeated charging has on the same four batteries and update.