any use for a car battery on board -

[dunkelly]

I have access to newish 80amp car batteries ,which i know are not deep cycle but was wondering if there can be any good use of them on board and what the pitfalls of connecting it in with my normal domestic batteries .

 

[Kelpie]

I have access to newish 80amp car batteries ,which i know are not deep cycle but was wondering if there can be any good use of them on board and what the pitfalls of connecting it in with my normal domestic batteries .

Should make a perfectly good engine start battery, as it is doing the same job.
If you want to use them as a domestic bank, best practice is to start afresh rather than add them in to an existing bank.

 

[dunkelly]

i was thinking of adding them as a second domestic bank still charging from the alternator but soley running the fridge / heater

 

[Spyro]

By access do you mean free? If so just use them until they are done. They aren't deep cycle so wouldn't stand as much capacity draw or recharging but if they are free 80ah is 80ah

 

[prv]

Most bog-standard “leisure” batteries are barely distinguishable from car batteries anyway, I suspect.

Do consider whether your additional batteries are truly a “separate bank” though - just putting them in a different locker won’t make it so . If there’s a plain copper path between them (even if that path happens to travel via the engine bay and back) then they’re not actually separate.

(Note that doesn’t mean don’t do it, just be clear whether you’re extending your existing bank or adding another.)

Pete

 

[oldharry]

Depends how voltage sensitive the equipment you are using is. Car batteries are designed to give a burst of power then be recharged. As they discharge voltage drops away fairly quickly. Even basic leisure batteries hold their voltage better, but are less resilient than true deep cycle designs to being deeply discharged. Each time they are run down to flat they lose a percentage of capacity. Starter batteries fail more quickly than deep cycle batteries if subjected to regular deep discharge.

 

[dunkelly]

As they are free i will give them a go , i will ensure i can completely isolate them and then see how long they last, i chose the fridge / heating based on the fact that initially they draw a reasonably large current then drop off . i was wondering what the effect would be if i put them together with the deep cycle domestic battery ie: deliberately put them together . anyone any ideas what the pros / cons would be

 

[All_at_Sea]

I find them very useful in the car, parked on the aft deck.

 

[geem]

We have truck batteries as domestic batteries. At the time the last set of useless sealed ‘leisure batteries’ expired, we had a very limited choice of replacement batteries, all at vast expense. We opted to install four 8D truck batteries as they were relatively cheap for their size and output. We are 24v so we have two pairs wired in series then paralleled up to give us approximately 500amp hr at 24v or 1000amp hr at 12v. They have been installed for three years now on a live-aboard boat in the Caribbean. This week I tested the cells with a hydrometer. All cells were identical and showing full charge. The four batteries weigh a total of 240kg. I think the secret to using these batteries successfully as a domestic bank is we never deep cycle them. We rarely drop them below 90%. We charge them up everyday and we keep them topped up with water. If you deep cycle car or truck batteries dont expect them to last.

 

[dunkelly]

i have always tried to keep my batteries topped up as much as possible like you and have often thought i may be damaging the deep cycle batteries - perhaps i should have gone this route before .

 

[JumbleDuck]

On my last boat I used a normal car battery for all my modest electrical needs, which included neither engine nor charging system. I carried a battery charger; very occasionally I'd be able to use it at a pontoon but normally I relied on my youth, beauty and hypnotic charm [1] to persuade hotel, restaurant and café owners to let me charge.

Those batteries took a hammering because I deep cycled the wazoo out of them, but still usually lasted five years or so. I went for "leisure" at first but then switched to normal car batteries and noticed no difference. A poster who worked in the battery industry said later that only the sticker varies between types.

In short: give it a go.

[1] At least I still have one of them, though sometimes I wish I'd kept the hypnotic charm.

 

[dunkelly]

okay taken all on board, i think i will add the car battery as a third battery connected into the system with normal battery size cable but with an isolator on the positive side so that i can switch it on when charging from the alternator or shore power and turn it off when not . i will connect the heater and fridge directly to it so they cant drain the domestic or starter battery. if this poses some problem i havnt foreseen would someone please let me know , thanks

 

[Kelpie]

I would be very wary of adding batteries into an existing bank. Any weaker batteries, with lower resting voltage, will draw power from the healthy batteries, which will damage them. General advice is to always start a fresh bank using the same type and size.

Most boats will have two banks, and only have them linked together when the engine is running and there is plenty of charging power available.

For your plan to use the car batteries to power only the fridge etc, you would really need to set them up as a third bank, which your boat presumably is not wired for. But I know some people add in dedicated batteries for their windlass or bow thruster, although I'm not sure how best to arrange that.

 

[dunkelly]

i agree with your thoughts , i maybe wasnt clear that i intended to do just that . the third set would just be charged from the same charging routine and not connected to the boat general supply . part of the reason for supplying both the fridge and heating was that they both recommended and are supplied directly from the battery making it easy just to switch them over to the third battery .

 

[richardabeattie]

As a Scots Presbyterian economist I have been running my boat for the last twenty years on second hand car batteries for engine starting and domestics. I take them home for an occasional reconditioning charge and I always have a third one in the car just in case.
On the down side some of these batteries have cost well over £10 and once or twice they have lasted less than four years.

 

[Heckler]

On my last boat I used a normal car battery for all my modest electrical needs, which included neither engine nor charging system. I carried a battery charger; very occasionally I'd be able to use it at a pontoon but normally I relied on my youth, beauty and hypnotic charm [1] to persuade hotel, restaurant and café owners to let me charge.

Those batteries took a hammering because I deep cycled the wazoo out of them, but still usually lasted five years or so. I went for "leisure" at first but then switched to normal car batteries and noticed no difference. A poster who worked in the battery industry said later that only the sticker varies between types.

In short: give it a go.

[1] At least I still have one of them, though sometimes I wish I'd kept the hypnotic charm.

Hilarious!!

 

[Biggles Wader]

As a Scots Presbyterian economist I have been running my boat for the last twenty years on second hand car batteries for engine starting and domestics. I take them home for an occasional reconditioning charge and I always have a third one in the car just in case.
On the down side some of these batteries have cost well over £10 and once or twice they have lasted less than four years.

I do much the same. Im not Scottish although my name might suggest otherwise:encouragement:. Both my batteries are over five years old and one of their replacements is in use in my car, a domestic battery from a campervan given to me by someone going touring who bought a new one just in case. I have a couple of spares from scrapped cars in my shed.

 

[dunkelly]

a few more thoughts on this , is it ok to mix sealed and unsealed in the same system and is there any convention about placing bow to stern or athwartships as all the boats i have owned have always placed batteries athwartships

 

[geem]

a few more thoughts on this , is it ok to mix sealed and unsealed in the same system and is there any convention about placing bow to stern or athwartships as all the boats i have owned have always placed batteries athwartships

I have 7 batteries onboard. They face all different directions. It makes no difference