I'm not saying parallel installations can't be used--only that they shouldn't. Even GE, in their commercial battery manuals, says that if you are going to parallel cells/batteries the preferred method is to parallel the CELLS and then stack the parallel cells in series, rather than paralleling the assembled batteries. This is because there will still be real potential for problems associated with charging and discharging if there is any one bad cell, or any voltage/resistance variation in each battery.
But when you say paralleling is NECESSARY for boats...what kind of boats do you have in mind? I can get you 12V batteries rated for over 1600AH @ 12V from commercial vendors, such as:
Item # Ah@20hrs Weight (lbs) Size (inches) (L x W x H)
15-799 627 498 30.75 x 7.78 x 23.25
15-800 732 558 17.89 x 12.96 x 25.0
15-801 836 630 20.16 x 13.0 x 25.0
15-802 941 696 22.38 x 12.97 x 25.0
15-803 1046 762 38.96 x 9.01 x 24.88
15-804 1150 840 27.12 x 12.97 x 25.0
15-805 1255 918 29.82 x 13.48 x 25.0
15-806 1359 984 31.58 x 13.0 x 25.0
15-807 1464 1068 33.65 x 13.0 x 25.0
15-808 1568 1128 35.95 x 13.0 x 25.0
15-809 1673 1260 38.96 x 13.51 x 25.0
List Price: US$2,649.00 includes free motor freight delivery within the US to a business address.
from the first hit on Google at:
claiming "With proper maintenance, these cells will last 15 to 20 years. Cycle life expectancy is 1500 cycles to 80% depth of discharge, or 5000 cycles to 20% depth of discharge." The vendor, "Real Goods" has a good rep but they are NOT battery manufacturers or commercial vendors, prices will be deeply discounted for similar batteries at your local industrial park.
and they DO come bigger than that. Incidentally, if you buy these batteries UNassembled, they are built from standard 2.2V cells that can be lifted by a single human and configured into odd spaces/forms as well.
How many of use really sail with more than a 1600AH combined battery capacity? (Now now, submariners don't count!)
With a parallel setup, you simply have the opportunity for more new problems that just don't exist in serial installations. Sure, it's an EASY way to buy your batteries at the local K-Mart...its just not "best of breed" practice.
"If the charge voltage is correct, you should not be boiling off water." Assuming that the whole boat is at 70F or there is a temperature compensation lead or sensing in the alternator. Normal charging, deep charging, without temperature compensation may occassionally boil off water.
"Measure the voltage of both batteries during a heavy charge (or discharge), they should be the same measured with a 3 ½ digit voltmeter."
Yes, but unless he has a Fluke-quality DMM...Typical numbers from a "consumer" grade DMM are +-2% with a float of 2LSD on the DCV scales.
That means 12.60 volts "displayed" can be off by 2% either way, plus or minus a float of 2 digits in the last column. So 12.60 on the meter can mean 12.32 to 12.87 volts is actually being measured. 12.34-12.85 more probably.
That's not to say the DMM isn't valuable...but when it can be reading "12.6" while the actual battery voltage is 12.34-12.85....a grain of salt is needed in analyzing the results. The meter can't be taken at face value, unless it is calibrated or checked on something else. The variation of 0.6 volts is HUGE when we consider that a nominal 12V battery only supplies useful power over a 1-volt range.
I think we can both agree there are better and worse ways to do things...with variations in how we each decide what 'better' and worse mean. And that there's alot of room for practicality versus finesse in 12V systems.
Paralleled banks work, sure. Most of the time. And when one battery goes bad--everything goes bad. I just don't trust them to be left alone, working in the dark, skulking under the quarterberth, without human supervision that way.