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

Geoff Schultz

Salomon Fringe wrote in
:

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?

Perhaps your conclusion should be that you should have invested in a good
charge controller to make sure that you don't charge at 15V. If you're
investing in AGMs, you should invest in the rest of the necessary
components also.

You should also learn that you shouldn't deep cycle any batteries. I try
not to have mine drop below 12.3V and typically keep them at 12.5V and
above.

-- Geoff
www.GeoffSchultz.org