Bad Battery?

[bobcinga]

Was out on the boat yesterday and was sitting at anchor for about seven hours. Did not use genset. Refrigerator, Raytheon c80 (no radar), vhf radio and radio (nothing special), were on the whole time. Several bathroom flushes, but that’s it. Went to turn on blowers and nothing (in fact draw made c80 turn off). Checked 12v meter in the panel and when blowers were turned on needle dropped down to 8v. Refrigerator draws 4.4ah and radio etc should draw less than 2ah. Battery is about a year old. Rated at 105ah c20. Battery hydrometer (?) was showing green. I had a problem with another battery not working right out of the box and had to return it. Battery charger showed charging at 3 amps last night and is at 0 this morning. After about an hour charging back at the dock, tried battery again running blowers and refrigerator (charger off) and it held a little above 12v for 5 minutes of testing.

Any thoughts or just another bad battery?

[bud37]

It really seems like you just ran the battery down.....Consider, you only have one battery which may not have been fully charged then 6-7 hours with approx 6 to 7 amps per hour for a draw of 6x7=42 amps out maybe more. Now that 105 Ah at 50 % would be around 52 and you were down to 63 Ah capacity left. Blowers pull a high load so I see nothing unusual IMO. Real world numbers are probably different.

Just to add , I am assuming that this is a deep cycle battery you have .

You need more Capacity for days like that......

[km1125]

Source of the post
.... and it held a little above 12v for 5 minutes of testing.

Where were you measuring the voltage? If it was right at the battery, then something is wrong with the battery. If it was anywhere else, like a voltmeter on the helm or electrical panel, then I'd suspect a bad connection somwhere. With that little load for 5 min you should have been at 12.6VDC.

[bobcinga]

It was at the meter in the dc panel. Could have been 12.6. Meter is not that accurate in my opinion. Just trying to get across that needle didn’t move. When other battery failed out of the box I could turn on key and watch the needle fall straight off. That one was for an engine.

[km1125]

I'm inclined to go with Bud's idea that the battery was just worn down.

When you say the battery charger was only showing 3 amps overnight, was that just for the house battery or that's the total charger output to all batteries? Where there ANY DC loads on at the time? (they would/should show up as a "charger" current)

On the panel meter, can you tell the difference when the batteries are under a charge (at 13.6-14.2VDC) vs when they are not but are fully charged (12.6VDC)? If not, you should add a digital meter so you can tell for sure. Even a very cheap one will do.