BoatBanter.com - View Single Post - Batteries - what's best and cheapest for long term cruising these days

Salomon Fringe

wrote:

On Mon, 16 Jun 2008 13:06:47 +0200, Salomon Fringe
wrote:

wrote:

Here's a fun little practical application demonstration that Salomon can try for
himself:

Take a group 31 flooded deep cycle battery of whatever brand you think is the
best, and any group 31 AGM battery off the shelf regardless of brand. Attach a
12 volt headlamp to each and let them sit with the headlight burning until it no
longer glows at all, indicating the batteries are flat.

Now, wait 30 days, and THEN recharge both batteries using whatever method is
recommended by the manufacturer.

After charging, load test both batteries. You'l find the flooded battery is now
a heavy piece of junk, but the AGM performs pretty much as it did before this
torture test.

Good. Now you do the following experiment. Tkake the same group of deep
cycle batteries and AGM batteries and put them on a charger at 15V.

Wait just one week, and THEN test both batteries. You'l find the AGM
battery is now a heavy piece of junk, but the flooded battery performs
pretty much as it did before this torture test.

After you did this test, stop and think what which of these two torture
tests would be the more likely that a battery installed in a cruising
boat will ever have to face.

What is your conclusion now?

Most charging systenms have regulators, and there is no reason why you
would charge an AGM at 15 volts unless you were an incompetent
idiot...

Oh, wait...

nevermind.

Why is draining batteries empty with a headlamp and then leaving them
like that for a month more competent than charging an AGM at 15V?