Deep Cycle 12V Batteries

A bit off the "run of the mill" questions but with the quality of the contributors I was hoping someone could advise with my other hobby which is sailing.

I have a boat which I regularly use for long periods away from a 230V supply. It has three series 24 size 12V lead acid batteries (about 85Ahr each) for low current service use - ie powering lights, a fridge, electrical instruments etc. I have previously used "Leisure" type batteries but am only getting at most two years of life from them and end up running the boat engine on a daily basis to recharge them (with the help of a clever alternator controller to give a three step charging regime).

I am looking for a cost effective flooded lead acid battery (this rules out AGM and Gel versions).

Does anyone have any experience on makes and models of this type of battery. I am currently looking at the Crown 24DC95 deep cycle units - has anyone used these before?

Other size batteries are not really practical as there are space restrictions which prevent larger batteries being fitted.

Many thanks in anticipation

Steve

Have you contacted Crown and asked them about your particular application?

I should point out that battery manufacturers claim all sorts of things for batteries that are never realised in real life. Guarantees are virtually impossible to claim on as there are all sorts of get-outs - even the best most expensive battery companies have clauses and small print which makes it very, very difficult to make a claim.

Crown say they use 10% thicker plates than their competition and do say this battery is suitable for this use and on paper they look good, I would just appreciate the benefit of others experience.

Thanks

Steve

Have you performed any tests to see how much current is being drawn and what the terminal voltage goes down to after say 24 hr use etc?

Sounds like they are being worked too hard and being over discharged if they are only lasting for 2 years.

Our fridge certainly uses a lot of current but we have solar to help keep it topped up as well as the option to use it on gas.

Peter.

Peter, I have a battery usage and voltage readout and we use about 40Ahr/day and the voltage after two years of battery life is down to about 12.2V after 24hrs - 40Ahrs is about what I would calculate based on usage.

Bear in mind we spend a lot of time at anchor and are on shore power maybe once/wk.

Some years ago Halfords were selling car batteries with a life time guarantee , bought one for my Vauxhall after six years it was shot. Took it back to Halfords and they gave me a new one. Wow never seen an offer like that again.

Perhaps Halfords calculated that once a car had reached the point where a replacement battery was fitted then the vehicle in question would either not survive until a next replacement was required or that it would have changed ownership and guarantee was not transferable to new owner and hence no further expenditure. Probably this product guarantee was dropped after a few years so that their liabilities were reduced and the sales ploy had served its purpose.

Dave

The offer only lasted a couple of months but I passed the car to my son who in turn passed it to his uncle. Car and batt did another five years. Not bad at all.

Steve,

Presume the 85ah batteries are connected in parallel, in which case you have about 200ah of useful capacity which should give about 5 days to get to the 2.03v/cell which you have got to assuming they were fully charged at the start.

Have you tried disconnecting the fridge and other loads with an ammeter in series with the + 12v o/p to check whats using the power? Its also possible for the alternator to develop a fault which can cause an unseen current drain.

The leisure batteries should give you a far longer life than car batteries especially if they are rated for semi traction/deep discharge use. Normally the manufacturers specify the number of cycles for the life but generally the thicker the plates and the heavier the batterys are the better until you end up with fork lift type batteries..

Peter

''Tis not ideal to connect lead acid batts in parallel, if one is a bit down you could get large currents between the two if alternator diodes go leaky yes the batt can dis charge thro it. On my sons metro the diodes burnt out causing fire sparks and smoke under bonnet. Reduced the alternator to a pile of scap .so far modern cars don't have these probs.

Traction batteries are better than leisure ones for deep drain applications.

Hi Steve

You say they are used for "low current service use" but then mention the fridge which is one of the biggest draws of current on a leisure craft. You do not say what type of boat you have, this may help. I normally get seven years from a set of batteries and only buy the cheap ones from a caravan superstore and use a Halfords one for starting.

Also what type of fridge do you have, an absorbing one or one with a compressor, this can make a big difference.

I would check out the boats electrics before blaming the batteries.

Les

Bear in mind that lead acid battery will only take in a charge what it needs, overcharging can make them boil!

Long trickle charging is not to be recommended and this will happen with Solar cell application. I know someone will refute this but trickle charge makes soft layering on the plates and leads to sulphation, a battery killer.

Adequate battery capacity for the tasks it is asked to perform is also a significant criterior.

My Sons Yacht has sat nav steering and it takes a lot of power to run the motors for the hydraulic steering and on a long voyage needs the engine running for 3 to 4 hours a day and it barely makes it through 24 hours including Solar cell operation during the daytime.

Clive

I know far too much about mistreating lead acid batteries! In my youth playing amateur radio included spending the odd weekend in a hill-top tent with a battery powered transmitter, lights etc. Turns out that's a very good way of destroying a decent car battery; they really do not like being discharged completely.

Deep discharge types are much better on a hill-top, but you still have to treat them right. They do not like being:

• discharged below about 12V,
• overcharged,
• recharged too quickly,
• discharged too quickly

Could any or all of these bad things be happening on your boat? For example, if the battery volts drop too low, and the generator is run for a quick recharge, and the batteries end-up slightly overcharged, then those batteries will have a short life. Battery Management Systems were too expensive for hobby use in 1985. I dunno what's available today.

Dave

On the basis that car batteries are on charge all the time the engine is running, and the battery on my last car lasted 12 years from new, a modern alternator and regulator system doesn't seem to damage the battery by overcharging. Of course I don't know how modern your boat set up is. the charge current should drop to pretty much zero by the time the battery reaches 14.4 volts. As SoD says, what does damage them is over discharging. I've seen various figures, some say don't use more than 45% capacity, some say don't go below 10.5 volts. These are not the same! Perhaps more than 45% causes small cumulative damge, less than 10.5v does it more quickly. No doubt someone will know.

According to **LINK**

a modern fridge uses 1 kWh per day, which is near enough 80 Ah at 12v. I'd look at buying a gas fridge, massively reduce your electrical energy needs

Hi Steve, I was in your position on my boat and as well as having a windy generator I also fitted a Sterling alternator 'smart' regulator which helped with keeping the 3 x 110ah (domestic) leisure batteries fully charged. As Neil says, traction batteries give a good life, but if you read what Charles Sterling (of the Sterling regulator and other electronic stuff fame - google him) has written about lead acid batteries then 2 years is about all you can expect from bog standard lead acid batteries. Seems like the alternatives are buy the cheapest deal you can at the time and replace every 2 years, or pay a lot more and replace every 3-4 years - if you do the maths the end costs are remarkably similar!

Doesn't help much I know!

Chris

The open circuit voltage of a lead acid battery is a good indicator of state of charge (SOC), provided the battery temperature is taken into account. The other big proviso is that the battery needs to 'rest' before making the measurement. We normally allowed 5 hours before taking voltage readings.

Charging is simply constant voltage, 2.45V per cell at 20°C, lower for lower temperatures and vice versa. DIscharging a battery is not a problem, provided it is not left in a discharged state. Generally a rested battery voltage below about 10.8V is regarded as fully discharged. Percentage capacity doesn't come into it. On our last hybrid vehicle we were running the batteries at about 40% SOC. Otherwise regen causes the battery voltage to rise excessively and the energy goes to waste. Over-voltage and over-charging leads to hydrogen formation and venting, which is generally a bad idea. Transient high and low battery voltages can be as low as 6V, or as high as 18V for a nominal 12V battery. But they are just that, transient, usually a few seconds. On a hybrid vehicle regen and drive currents can be low hundreds of amps for relatively small batteries - around 15 to 25Ah.

Running batteries in parallel is a sure fire way to badger them. The batteries will not be identical, so over a relatively short space of time the batteries will drift apart in terms of SOC, leading one battery to be over-charged, or undercharged. Ultimately you can end up reversing the voltage on one cell, which will kill the battery.

The characteristics of the battery are determined to a large extent by the internal construction and materials of the battery. A float battery (burglar alarms) is intended to sit on float charge for significant time periods. But other batteries (leisure, deep discharge) are designed to be charged and discharged on a cyclic basis, with no float.

What one really needs to control to keep batteries in good order is SOC. To that end the last battery management system I designed had provision for charge and discharge of individual batteries, independent of the charge/discharge of the series string.

Andrew

I am curious as to why you don't want gel or agm is it because the ones you have are used as starter batteries as well ?

i run an ultimate brand (usual disclaimer applies ) in my boat that sees intermittent use and it is set up with a smart charger to keep the battery charged , been going strong for over 3 years without a problem .

I previously had a lead acid deep cycle unit and it died inside two years - sulphation issues .

Alternators will not fully charge a battery , you need a dc - dc charger as it can fully charge a battery from an alternator supply - used a lot in 4wd circles .

What sort of low battery voltage warning or cut out do you have ?

How old is the fridge ? You may find a newer unit more eficcient .

Ian

Having two sheds full of motorbikes that tend to sit for long periods unused between rides, I have given up on the old acid slopper batteries and gone to all AGM and leave them hooked up to a smart charger between rides. They seem to last two or three times longer, at least. Mate had one last for seven years, vs one year for the old acid sloppers with no smart charger.

Why does nobody use NiCad cells now ? They would be my choice for your requirements. Not that I know much about the subject. My electric fence uses cast -off car batteries and a solar panel, seems to last years, but very low current draw.