Fried batteries...

[MiVelero]

Ok on a previous thread HoffaLives asks does everyone learn the hard way?
I DO!!! I checked my two house batteries 12v 90a @ and they were bone dry... OOooops!!
The starting battery 12v same thing, but fortunately my two 12v batteries for refridge are fine. All were installed 3 years ago. They were a bit neglected and tottally discharged after Katrina... the boat was floating no obvious damage and the waters too nasty to even approach, figured batts were the least of my problem then.
Last time we used them was a month ago we were out for 3 days with no obvious power problems.
I have checked level often, but lately I had only checked the refrg batts since they are easier to access and are used more(fridge allways on) I figured these would loose fluid faster. If these were fine then the others should be fine also. WRONG.
After reading many of your posts on the subject I opted to replace my house bank with two Trojan 605 golf cart batteries and a 12v 1000a for starting.
Now I have two questions...
Many say a battery should not go below 50% before recharging, How does one know when this 50% is? How is this measured?
The boat is on shorepower batteries are on charge with Guest chargers ... house bank @ 30a - frdge @ 20a - start @ 15a.
Would the charger allways on be detremental and should they be run down periodically or atleast charger off for periods of time ?

Thank you

[sailingdog]

If you've got a volt meter attached, 50% discharge is roughly 12.0 volts.

A fully charged 12VDC battery will give you 12.6-12.7 VDC. A 12VDC battery at about 50% charge will read around 12.06VDC. You can see at table of the various voltages and charge states here.

This is only a rough guideline, and may vary a bit depending on what brand batteries you have and how old they are. Having the charger always on at the dock is probably better than having the batteries run down too far, provided it is an intelligent three stage charger. However, considering that your batteries were dry... it sounds like the charger may be having some problems and regularly over-charging the batteries...causing the electrolyte to boil and the water levels in the batteries to drop. You may want to check the voltage levels of your charger once the new batteries are in place.

[Faster]

Highly recommend the various battery condition/usage monitors around these days, the Link 10 being the most basic and inexpensive. Properly programmed, these devices to a nice job of keeping you informed of the state of your amp hour bank.

You really do have to check battery levels frequently, even with today's "smart chargers" if they are always on shorepower and charging.

[sailingdog]

The Xantrex Link 20 will monitor two battery banks, the Link 10 will only monitor one. Sailor Solutions also has a battery bank monitor that is fairly well regarded in the PS magazine reviews and fairly reasonably priced.

[camaraderie]

I would note in passing that an instantaneous reading of voltage either shortly after or during the operation of DC equipment does NOT give a reading of true battery state of charge. The battery must be completely at rest with no loads on it for several hours (even then the reading will be slightly low). the only practical method for getting a proper charge/discharge cycle state is with a Link10 or similar setup which measures amp hours in and out. Cheaper than new batteries!

[sailingdog]

Also, applies to having the battery charger on... if you turn off the battey charger and disconnect all loads... in a couple of hours you can get a fairly accurate voltage reading.

Originally Posted by camaraderie

I would note in passing that an instantaneous reading of voltage either shortly after or during the operation of DC equipment does NOT give a reading of true battery state of charge. The battery must be completely at rest with no loads on it for several hours (even then the reading will be slightly low). the only practical method for getting a proper charge/discharge cycle state is with a Link10 or similar setup which measures amp hours in and out. Cheaper than new batteries!

[StoneAge]

There's a product from wizbangplus.com that I attached to my old 8 D's and they have been brought back to life. It's about a $25 doink and just might save a bunch of money in replacement batteries. No, I don't get anything from them. Just a happy customer.

[MiVelero]

Thank you all for your coments and suggestions.
At present I have a guest system voltage scanner for up to 4 batteries. I am looking for something that gives me current levels (amps) sounds like the Link system might be the one.
My old batteries did get down way below the 50% more than once... I guess that could have sped up their demise.
Thanks again.