Battery Charges

[Aunt Bea]

I have a new 23/IV and had it rigged for shore power.  However I have 2 AGM batteries and am trying to figure out what types of charges would work with the AC to charge the DC batteries while hooked to shore power.

Any ideas...help....Thanks,

Aunt Bea

[curtis]

Aunt Bea,

AGM batteries cost a lot more than the cost of a good charger, and a bad
charger can shorten the life of your batteries.  Don't use an automotive
charger unless you want to be buying new batteries every few years.

Some very good chargers are made by Xantrax and Guest.  The Guest tend
to be a little less expensive.  The higher cost chargers will charge your
batteries faster.  For example a 20A charger would charge two 105 AH
batteries from 1/2 charge to near full charge in about 5-6 hours and full charge in about 8 hours.  A 20A charger will set you back about $300.

If you aren't concerned with bringing your batteries up from 1/2 charge overnight, then look for a smaller charger.  A 10A chareger will take twice
as long to bring your batteries to full charge, but it will cost you $130 and
do the job just fine.  If you don't drain your batteries down very far anyway
(which will make them last a lot longer) then a smaller charger would be
just fine.

You could go to the next step down, a 6A charger and get the price well
under $100.  Guest has a fixed mount 6A charger for about $85.  This is
quite small for two batteries and best used with some other charging
source.  You're better off with a 10A charger.  Look in West Marine or
Defender or Sailnet or most other online marine suppliers.

You can leave one of these chargers hooked up to the battery and plugged
into shore power indefinitely without hurting the battery and the float
charge will increase the life of the battery.  If you did that with an
automotive charger or bargain charger, you'd overcharge and ruin the
battery.  Avoid leaving a battery for months at a time without charging
and always charge right away after discharging.  Well cared for batteries
can last 5-10 years.  Neglected ones can last 2-3 years.  At $200 a battery
for AGM, you'll want to get as much life out of them as you can.

Curtis

[Aunt Bea]

Thank you Curtis,

Well my husband told me I was wrong on the batteries...go figure.  They are cranking batteries.  Flooded cell, maintenance free.  They are not dual purpose either and there are two of them.   We have an electric start on the outboard so I guess that is why Com-pac put those in there instead of the other.  Will the recommendations you made still work for these?  Should we sell those and invest in a dual purpose?  I never know you needed to become a mechanic to sail a boat.

Thanks again,

Aunt Bea

[curtis]

Aunt Bea,

Whether you want to replace your batteries depends on what you want to use them for, or if you want batteries at all.

If all you use them for is electric start on the outboard, leave them alone.  Get the better charger anyway and if you ever replace them it is worth it.  The better charger will also prolong the life of a starting battery.  Two batteries is quite a lot to start an outboard that certainly also has a pull chord as backup.

If you sail at night or anchor where you have to use an anchor light or have fixed mount VHF and/or fixed mount instruments (knotlog, depth, fixed mount GPS, etc) then you have a light to moderate load.  An AGM or flooded deep cycle battery would be better suited but even if you have two car batteries no sense replacing them now unless you think you can sell them and get a reasonable price.

If you have a heavy electrical load, such as refrigeration, watermaker, air conditioning, then definitely replace the batteries.  You didn't mention any of this sort of stuff so it unlikely that's what you are using the batteries for.

If you aren't using the batteries for anything except starting and an occasional brief use of the lights, you might want to take one out just to reduce weight.

So best bet is probably leave the batteries there and go out and get a decent charger.

Curtis