SHETLAND OWNERS ASSOCIATION

Hello Forum.

After any advice regarding battery issues on the boat if anyone can help?

I have three 110 amp batteries fitted, and a Strling 12v 20 amp battery charger. The boat also has a NASA battery monitor.

The battery charger is run via 230 volt shore power.

The batteries were new at the end of May this year.

A couple of weeks ago I noticed the batteries were taking a longer than usual to charge to 100%.

We had a night away on the boat on Friday. The batteries were showing 100% when we moored up. After only five minutes of running the Outwell 24 litre cool box via the 12v system, the batteries had dropped to 12.8v. The coolbox was only plugged into the 12v ocasionally to try and maintain battery power but even using this strategy, the batteries wer showing 12.6v by Saturday afternoon.

Any ideas?

Hi,

I'm not an expert but I always understood that you charge batteries with 13.8v and they show 12.8v when full with the charging system disconnected, and are considered in need of charging when they drop to about 11.5v.
You haven't said whether you have deep cycle leisure batteries or standard auto batteries. It does make a difference to the lifespan of auto batteries when used with leisure circuits instead of their designed use of engine cranking and constant alternator charging.

Chris

Hi Chris.

Thanks for your reply.

The three batteries are Britmarine 6110DT 110amp dual purpose sealed, designed for deep cycle lesuire and starting.

My concerns are that, given 100% full capacity is 12.8v, over the first couple of months they would maintain 12.9v, then gadually drain according to use. Considering the draw was off the three batteries (they are linked together per Shetland fit out from new) the volts drop dramatically now after only a few minutes. When the Outwell is disconnected, the voltage will recover a little, only to drop again significantly next time the coolbox ix plugged in.

The other issue is the longer charging period now required to get 100% charge.

A friend who uses the same Outwell coolbox on hs single 110amp battery can run his single battery for eight hours for only a few volts drop.

Simon.

Are the batteries connected in parallel as a single bank? If so a single duff cell in any battery will drag the whole bank down over time. It may be worth charging the batteries then disconnecting them from one another then checking the voltage on the separated batteries with a voltmeter after a day or so.

I agree with vreagh and would also suggest fitting switches between batteries, so they can be isolated from each other, to check which one may be causing your issue.
Also I would keep one on a separate circuit, for starting engine(s), to act as a backup should the others fail.
Cool-boxes can draw a lot of current and just because your friends isn't giving issues, doesn't mean yours will behave exactly the same.

As dellquay13 says I would worry about such a small drop!
Most electronics will signal/alarm at around 11.5v but should still work ok.

Hope you find what causing it.

Thanks for the replies.

The boat does have a battery isolator switch as fitted by Shetland from new.

Technically batteries 2 and 3 are paired (they are connected together by a positive and negative lead). Battery 1 technically is either starter or additional domestic battery. Position 3 runs all three batteries.

However, I can't isolate between the paired and starter battery via the switch, even with just the starter battery selected, I can use all 12v equipment.

The switch has been tested with a multimeter and the switch is working correctly. I did remove all the positive leads to the three batteries for a couple of days to see if one of the batteries was faulty (couldn't imagine three new batteries being faulty). When tested with a multimeter they all read within 0.1 of a volt. I had read about wiring issues with Shetland 27s but couldn't find any further details of what the problems were.

As mentioned, my thoughts are a duff battery charger that has over charged the batteries and knackered them, or less likely, three duff batteries (new in May)

The battery monitor is a NASA Clipper fitted from new by Shetland. It gives a real time digital volt level reading and a bar scale giving a % of battery charge.