T&T: Batteries

[Candy Chapman and Gary Bell]

Don Sorensen asked:  
<snip>
I found that wet cell golf cart batteries are the cheapest to buy.  They were
around $150 (less boat show price 0f 15%) and were about 200 amp  hours. With
my ten batteries I would have about 1000 amp hours for $1,350.  

The Rolls varied from $350-500 dollars for each ten year life 240 amp  hr.
wet cells. Special caps were an additional $20 for each cell. So a bank  of
these would run about $3,500 - $5,000 depending on the amp hours.   

Then there were the AGM Lifelines, Meridians etc. These ran almost  $650
each, however being 12 volts, I would only need 5 of these. Again  these
would cost about $3,500 but require no maintenance. 

Using  these as ball park cost, amp hours, life span etc, how does one
justify the  leap from the basic golf cart batteries to the hefty Rolls or
the AGM  Meridians?

I would be interested in any of your thoughts.

Don  Sorensen
M/V Esperanza
60  DeFever

R. Lee suggested:

I justified my jump from wet cells to Lifeline AGM's by my arthritis. I  
didn't want to crawl around watering or de-corroding batteries anymore. One  lives 
but once.
 

My reply:
Don't forget that the difference in cost, while it is quite substantial 
now when you write the check, will in the end be amortized over let's 
say ten years.  Then the cost difference can be seen as being only one 
tenth the initial difference for each of those ten years.   You will 
also get ten times the savings in annual maintenance stress -- much less 
work in each of those ten years, likely only a look-see with a 
flashlight and ordinary voltage/discharge current monitoring.  My 
advice, if you can stretch to cover those lofty up front costs for the 
AGM rig, go for it.

BTW, you know not to routinely charge flooded cell and AGM batteries 
from a common charger?  I know, some of the battery makers claim it is 
OK, but you will not get the fast charge for the AGM's while 
overcharging the flooded cells that way.  You can pretty freely 
discharge flooded and AGM batteries together, particularly  for short 
times, like starting an engine from the house bank with a combiner (or 
jumper cables, if not too long).  You also know not to charge multiple 
banks with an isolator, because unlike the relay based combiner (without 
significant resistance or voltage drop across it), the isolator uses 
diodes, which have a built in half volt drop.  Thus the battery on the 
far side never sees full charger output and the charger cannot 'see' the 
condition of the isolated battery.  Also, always use temperature 
probe(s) right on the house bank so the charger can control it's output 
to match the battery condition at any given time. 

The AGM technology is well and truly sealed, so you should have NO 
corrosion from battery fumes/spill.  My company's first several 
generations of laptops (HP's, in the eighties) used Gates AGM 'D' cells 
inside, with absolutely no leakage or corrosion ever, after all the 
tough treatment we dished out.  AGM batteries accept and release charge 
significantly faster than flooded cells, allowing high rate / shorter 
charge cycles and heavier short term discharges without problems.

 With all due respect for the lusty, robust Rolls outfits, don't think 
they will completely free you from inspecting/corrosion control chores 
-- you will still have to open each (moisture retaining  but still 
vented) cap and hydrometer each cell.  Although you will see much less 
water loss, and the corrosion will be much lower, you are likely to find 
a little still present enough to warrant regular inspections and topping 
up.   All that robustness means heavy too.  For those of us with 
ballasted trawlers that's perhaps even a good thing, but for my power 
catamaran, weight as well as balance/location are very much more important.

The usual disclaimers apply.  I have no financial interest in any of 
these choices, beyond being a present and future consumer.  My interest 
grows from the fact that I am facing both a battery and a 
charger/inverter replacement, with the attendant opportunity to tidy up 
some design issues.  I have selected a Victron charger/inverter and I 
will retain the combiner PDQ fitted.  I will replace both the start 
batteries (with AGM starter type) and expand the house bank (with 
several AGM deep cycle).  The engine start batteries normally will 
charge independently from each engine's alternator, but since I want the 
ability to charge them through the combiner from the big house charger, 
and I don't want to crawl in to fuss with them either, I will want AGM 
engine start batteries.  I will also be moving the windlass over to a 
much upgraded genset start battery up forward, with a dedicated remote 
charger, and if I can afford it will use AGM starter type there as well, 
as I have the heavy cabling PDQ used to power the windlass from the main 
circuit board to use with my combiner.