# What size battery do I need for a fish finder in kayak



## Arand18

Hi im new to this forum, I am wanting to get a fish finder for my kayak as in about 2 and half weeks im going on a week long fishing trip, I want to get LOWRANCE MARK 4 Chartplotter Fish finder Combo, in my kayak I have a space for about 2 large battery's as later I will also want to get a battery for a small electric trolling motor, so what size voltage and amp hour do I need to run this fishfinder for 1 day, I can charge the battery every night so it doesn't need to last for a whole week.

thanks


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## bildad

:twisted:


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## Scott

Hi mate, i like a 7 amp hour but you can get away with a 4 amp hour. You can kill them if you discharge them to much so i went the bigger one even if it is a bit of a overkill as the weight increase was next to nothing. A trickle charger is better to charge them than a car charger a sit doesn't overcharge them and you can leave them on for a day or so without overcharging. A trickle charger should cost you around the $30 mark and you get them from the same place you get the batteries.


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## john316

I used to use a sealed motorbike battery, not as heavy as a car but still heavy as it was a good quality unit. I have stopped using it as I wanted to remove weight and have gone to the other extreme of using a battery pack consisting of 8 AAs. They last for several days but I am yet to experiment with rechargables. I only use a small depth sounder so I don't use a lot of power...

John


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## Glamo

Like Scott said I use a 7amp Hr battery with trickle charger all up cost about $70 you can leave it on charge for as long as your not using the yak works great. I got my setup from JayCar electronics, if there is a store near you check em out.


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## OldDood

According to the user manual for the Lowrance mark4 fish finder/plotter it requires a 10VDC to 17VDC power source and typically draws .75 Amps
Therefore if you want a fully charged battery to last for 8 hours you will need a minimum capacity battery of 8 x .75 = 6 Amp Hour (Ah) battery.
A battery of more than 6 Ah will last longer than 8 hours obviously.
A lead acid batery with an appropriate charger is probably the cheapest and easiest but like most rechargeable batteries if you discharge them below about 11vdc they will probably be permanently damaged and will never charge properly again.
Normally when I use any type of rechargeable in an application I use a device that automatically disconnects the load from the battery when the battery gets down to about 12 volts. This is commonly known as a low battery cutoff switch.
I would suspect that some fish finders automatically turn off when the battery voltage gets low but according to the lowrance spec. it will work down to 10vdc which will certainly kill a 12 vdc lead acid battery
Be aware that the life of most rechargeable batteries is only about 2 years and only if you have never over charged them or drained them too low.

I am not sure where you could buy a low battery cutoff switch from but I would suggest that you go to a specialist battery supplier and ask them for advice on what is the best battery/charger combination because it is a little bit tricky and they should be able to supply you with the correct gear.

Of course you could just hook a battery up to the fishfinder, which most people do, but you will find out soon enough that you will be replacing the battery quite often unless you are very careful not to run it too low.
Regards,
Mark


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## OldDood

Occulator said:


> As a confessed flat earther I reckon SLA is the way to go. And I reckon 4-7 AH is perfect for that sounder. I have that exact sounder and use a 4AH one and have never run out of juice. Used it for around 8 hours all up at Mulwalla last weekend and it only took me about 20 minutes on the charger when I got home to top it up. What's not to like?
> 
> They are cheap and cheerful, readily available everywhere, easy to use (fit in a standard Tupperware container), and best of all easy to charge. Just make sure you use an automatic type charger as the others will stuff it quickly should you forget about it for a few days.


Hi Occulator,
I love the flat earth approach and I am glad it works for you.
I know you are going to enjoy this article on the love and care of a 4Ah battery. http://www.silvertel.com/bat-technical-article-1.htm
Look how simple it is. :lol: :lol: 
I know i am being a wanker but an old electical engineer has to get his pathetic laughs anyway he can. ;-) 
Regards,
Mark


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## OldDood

Luv your work Gra.  
The technical info certainly cleared every thing up for the uninformed. ;-) 
I am not sure about your guesstimation on the sounder current draw as the production specification just says "typical 0.75Amps". Very strange engineering spec? Nonetheless you could be correct and your arguments are valid.
Seriously though, your product selection is excellent and would be ideal for any yakker with this sounder.
You can have an early minute tommorrow. :lol:

P.S. I do not have any electric stuff in my Yak. I do it for a living and it gives me the shits. I still seem to catch lots of fish though.


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## MrX

> " I'd get a 9800ma Lithium Ion (not Lithium Polymer as Mr X may point out should he care to say it one more time) for around 30 bucks from Ebay with a charger, http://www.ebay.com.au/itm/New-DC-1...ronics_Batteries_Chargers&hash=item35ba158e40"


OK gra: Go the li-ion, not the explodo lipo. (Where's sbd?)

With bildad on this one. Li-ion has it all over the trusty old basic SLA brick for electrical dummies (like me)

The "modern" battery has auto cut-off protection for: low voltage; over charge; and short (no need for a seperate fuse). The $20-$30 price for the li-ion *includes* a compact dedicated trickle charger, also with an auto cut-off to prevent overcharging.

The SLA has, um, well, it does work - it will run your sounder *and *it will start you motor bike.


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## MrX

Couldn't resist your siren's call, gra.

Choice of kayak batteries (like religion and politics) is one of those controversial topics that always gets the AKFF passions going. Don't sit on the fence like a girl - have an opinion (like bildad) - make a call!


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## OldDood

gra said:


> OldDood said:
> 
> 
> 
> I am not sure about your guesstimation on the sounder current draw as the production specification just says "typical 0.75Amps". Very strange engineering spec?
> 
> 
> 
> Yes of course, you could be well correct on that, it's a pretty loose spec. Apologies for suggesting it was a maximum, but you get my intent.
> 
> Gra
Click to expand...

No worries Gra,I knew what your intent was. The crappy spec in the user manual just annoyed me.
Anyway the LI-ION battery and charger you found on EBay kicks arse. Especially if it really does have all the protection features it lists in the Spec.
I have been contemplating setting up an LED flood light (waterproof, 120deg beam,10W, 12VDC, 700 Lumens) for catching bloodworms at night in the Yak.
The battery thing was giving me the shits and was a bit expensive, but I reckon I could probably do it for about $100 now. 
I might get around to it one day if I can get over my aversion to doing anything electrical when I am not getting paid for it. :lol: 
Good work,
Mark.


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## OldDood

Occulator said:


> MrX said:
> 
> 
> 
> Couldn't resist your siren's call, gra.
> 
> Choice of kayak batteries (like religion and politics) is one of those controversial topics that always gets the AKFF passions going. Don't sit on the fence like a girl - have an opinion (like bildad) - make a call!
> 
> 
> 
> I have to agree, make a bloody call will ya guys. I did. :shock: Ebay lions and $100 exploding lipos are for poofters and duncers, and ya know it. All ya need is a lousy $30 and you van be the owner of a black brick which will power a Massey Ferguson tractor (or a TR3) and last for years (well maybe two).. And any self respecting bloke with a shed already has a bloody 40000 milli-amp charger which can charge a tractor battery for Petes sake, so there's a saving right there.
> 
> But as always there's a catch. Cause when it comes down to it real men don't need batteries. Cause real men ain't afraid of the dark. :lol: :lol: :lol:
Click to expand...

Holy crap!! I have been doing this electrical crap for nearly 40 years and that is the most concisely researched, technically accurate engineering solution I have ever seen!
You are the grand master of electrical engineering Occy. :lol:


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## bildad

Righto mate, if you just want to run a sounder you have heard all the options available to you, should have cleared things up for ya :shock: 
Now you were saying you wanted to run an electric motor at some stage.
Basically your motor will draw 1 amp for every pound of thrust eg I have an Minn Kota 55lb motor, at full noise I will be drawing 55 Amps from the battery.
For this you will need a deep cycle battery (and it will run your sounder as well) now there are many deep cycle batteries out there, but I can safely say that there is only one type you need to concern yourself with AGM (Absorbed Glass Mat) you can install them upside down if you want to. You can get a deep cycle Lithium for the Job but it will be very expensive!!!!! 
The batteries are heavy I have a 120ah AGM weighs 32kg but I get 12 hours of fishing speed use out of it which exhausts the battery to 30-40% of its full charge, (same as SLA you don't want to run these flat).
You will also need a dedicated charger to charge the AGM Ctek are probably the best but I bought a Projecta and depending on what size battery you get will determine how many Amp charger to get, Rule of thumb is 10% of the battery size. 100 Ah Batt = 10Amp charger.
The other thing AGM has over other deep cycle wet cell batteries is their self discharge rates, A regular deep cycle will lose 3-5% of its original charge per week, AGM 5% per year and AGM charges faster as well.
There you go all the homework done for you. ;-) 
Now about that carton o Tasty Piss


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## bildad

Occy , I originally powered my first sounder Cuda 300 (lowrance X4 equivalent) with Metabo 10.8 Volt 1.3Ah lithium batteries and it would run easy 8 hours without backlight on. Not withstanding quality of the cells used in this el cheapo set up It would be certainly worth the experiment.


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## MrX

Occy, I recon a budding electrical expert could adapt the batteries from that drill to run a sounder.

Meanwhile, for us dummies, a fully assembled Rechargeable Li-ion Battery 12V 4800mAh, with charger = AU $15.42 delivered.

http://www.ebay.com.au/itm/Recharge...ronics_Batteries_Chargers&hash=item1e733c81f5


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## Zonbie

Now that's what I am talkin' about............. Excellent find, and thanks for sharing.

I'm off to buy me one now............ Perfect for my particular use.


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