Battery Issue

[Dick Pluta]

I can't believe that after many years afloat I have this newbie question. I don't know if it's testimony to my engineering skill that it's never happened before or testimony to my stupidity for allowing it to happen.

The electrical system in my Islander Freeport was in really bad shape when I bought her three years ago. Our boating season is short, only three months, so progress was slow, especially in the light of all the other repairs that took priority. This year I finally cleaned up the rats nest of electrical connections at the battery terminals by installing a nice, neat distribution sub panel, which really made a difference. Voltage at the instrument panel is a solid 14.1 instead of the variable low voltage previously seen. That was the result of a bad ground. Now everything is fine, except that last night, the lights got dimmer and dimmer and, finally blinked out and went dark. This made no sense whatsoever. Finally, I checked the water level in the batteries and they were low. Here's the newbie question. Can low water levels cause the batteries to stop putting out? I'd really like to hear that it can, because, otherwise, I have to look for the real reason.

Thanks

Dick Pluta
AEGEA

[Sailmonkey]

When we bought our boat the battery water level was halfway down the plates. The lights still worked, but the batteries were never the same.

[GordMay]

Yes, low water (actually electrolyte, about 35% sulfuric acid and 65% water solution) levels result in low/dead battery output.

The "ault" probably lies with your battery charging system.

Prolonged overcharging, or charging at excessively high voltage, causes some of the water in the electrolyte to be broken up (electrolysis) into hydrogen and oxygen gases, which escape from the cells. If the electrolyte liquid level drops too low, the plates are exposed to air, lose capacity, and are damaged.

See ➥ Trojan Battery Company

[djmarchand]

Further to Gord's post, when a battery is overcharged for a prolonged period, in addition the the electrolyite level droping, sulfate is formed which drops to the bottom of the battery. In addition to reducing capacity, if this sulfate layer builds up to the point of touching the bottom of the plates, the battery will then start to self discharge.

You may not notice this when it is hooked up to the shore power charger or the engine alternator is charging (although the battery will get real hot). But when you drop the hook and start using the battery, it will quickly discharge as you experienced.

So your batteries are likely toast and you have a problem with your charging system that needs to be investigated.

BTW 14.1 volts is too high for a float voltage. You should be reading somehting like 13.5 V. That may be another symptom of your overcharging. The root cause is likely your charger.

David

[Dick Pluta]

Thanks, Gord

I'm don't think the charging system is an issue. Right now, with all the work going on, we mostly sit at the dock and I have a good 3 stage charger. I also found it hard to accept that, unless a cell went bone dry, that the battery would just suddenly stop putting out. Right now I'm inclined to think that, while filling the cells, I disturbed (or, more properly un-disturbed) one of the other bad connections.I'm running off the starting batteries right now since the house battery is bad and will be replaced soon. I've fixed the worst of the mess,but there is still a lot of tidying up to do. I guess I just have to go bit by bit.

Dick

[Dick Pluta]

DJ,

14.1 is charging voltage under power on the water. Float voltage is 13.0. I haven't tried turning off the charger. I'll do that right now. That will tell a lot.

Dick