RO Water for Batteries?

[KnotYet]

Battery water should be free of all contaminants and minerals. You will keep adding water through the life of the batteries and the minerals will stay and become concentrated. 'Good' RO water may have up to 400ppm dissolved solids. Tap water can be far higher than that, or it can in some cases be quite low. The best RO water is around 100-150. Distilled water is zero, and deionized very close to that. I use the condensate from my dehumidifier, it is distilled water. One could catch the condensate from an A/C unit and save it - but be sure there's no debris or salt water getting into it. My T125's are in their 8th year of service on dehumidifier water.

Dehumidifier water contains whatever ions are suspended in the boat environment air.
There is no 'brine' component as there is with RO water. You know that residue that
ends up on surfaces inside your boat before you turn on the dehumidifier? It winds up
in the discharge tank. Then in some cases it winds up in the battery electrolyte.
Kidding aside, there's no comparison to distilled water. Dehumidifier water has no filter
to remove dirt and organics that are routinely airborne along with the moisture.
That being said, flooded batteries contain gallons of electrolyte and some impurities can
be tolerated for sure.

I don't know why you think dehumidifier water is the equivalent of distilled water.
There is an obvious difference between a closed, controlled distillation process
and what collects in the fins of a dehumidifier or A/C unit.

 

[koliver]

Anywhere in the PNW or SW BC, where rain falls a lot, the tap water is going to be very good. The rest of the world should use Distilled water.
I typically get 10+ yrs out of my FLA batteries with tap water.

 

[CharlieJ]

Not to keep beating the poor horse but:
The battery manufacturer recommends using distilled water and you can’t carry enough on board for an extended cruise/lifestyle. You have many recommendations in this thread for using an alternative to the manufacturer’s recommendation. Here is how to comply with the manufacturer’s recommendation:

Since you have a RO water maker and if you want to follow the battery manufacturer’s recommendations, then you can make your own distilled water on board. Use the RO water as feed stock (my rig typically produced 150 ppm TDS water), reduce the water-maker’s operating pressure per the operating instructions and manufacture water with a TDS << 5ppm. Reroute the “waste” water from this evolution back to your potable water tank. Easy peasey.

I did this for almost four years keeping my 1320Ahr bank of Trojan T105’s happy living on the hook in the Eastern Caribbean.

And, as always, YMMV.

 

[dhays]

I don't know why you think dehumidifier water is the equivalent of distilled water.
There is an obvious difference between a closed, controlled distillation process
and what collects in the fins of a dehumidifier or A/C unit.

I think the key here is, as you note, the controlled environment in which the distillation process takes. Both fluids are created through the condensation of the water in the air on a cool surface. So it just is a matter of the impurities in the air and any surface impurities on the condensing surface.

 

[foreverunderway]

I asked the same question on another forum when my membranes were new and I was getting under 50ppm. I was told no, absolutely not. Stick to distilled water, it's cheap and available in most places.

 

[CharlieJ]

@foreverunderway #35
Distilled water just isn't readily available in some parts of the world so RO water produced as I detailed in #33 is a perfectly viable alternative when you must top up FLA batteries.

So I am telling you in this forum that, yes, absolutely yes, double RO water with a TDS of <<5ppm is relatively easy to produce and is satisfactory to use in FLA batteries.

 

[foreverunderway]

@foreverunderway #35
Distilled water just isn't readily available in some parts of the world

I have no idea where in the world you have not been able to get distilled water, but in over 5 decades of seafaring on vessels of all sorts, I've yet to find one.

 

[CharlieJ]

Hard or impossible to find when we were in the Eastern Caribbean.

IYB.

 

[foreverunderway]

Hard or impossible to find when we were in the Eastern Caribbean.

IYB.

That's odd, as we've been cruising and chartering in the EC for the last 10 years and have been able to get it everywhere we've looked for it. Even on the tiny islands like Bequia and Union, Carriacou and Petit Martinique they have cars and trucks with batteries that need distilled water.
Even as far back as 1978 when I got here the first time, there were vehicles with batteries that required distilled water and it was available at one or more places on every island, or a day or two's wait for it to come over by ferry.
I guess there was some sort of international shortage of distilled water when you were here?

 

[CharlieJ]

I yield the field of battle to your superior knowldge and experience.

 

[FF]

I think many more FLA batts die from constant undercharging than a lack of distilled water.

The usual run from 50% to 80-85% SOC takes hours , with out wind or solar, the full charge seems to take "forever".