Boat Battery (not for motor starting)


New member
Hi All

Thanks for taking the time to read and reply. I am wanting to get a deep cycle battery for my boat. My motor is a manual start, so it will not be receiving any charge while on boat.

It will mainly run my fishfinder and then occasionally LED lights and I want to at a later stage at a cigarette lighter socket to charge a phone etc...

How many AMP hours is best value for money. What battery types should I consider (plate wise) and is a sealed unit (maintainance free) possible and a consideration.

Then charger wise, what should I take into account, does it matter what charger and how I charge.

Please excuse all the newbie questions and I hope I have given the info needed for you to assist me.


New member
Hi TKbaby

Most common size on the batteries are 100ah and 105ah.

Here you have a choice on going exide or Gel, but it will all depend on your budget. To keep things simple, the exide is "semi-deep cycle" and the Gel is "deep cycle". The "Semi deep" you will be able to discharge at 50% of the total ah rating and the Gel at 70-80%.

Summing this up in a nutshell
100ah on the "semi-deep" you will have 50ah of use.
100ah on the Gel you will have 70-80ah of use.

You also get the hybrid Gel which is a chameleon among these which are a mix between the exide and gel. You get them cheaper than true Gel batteries.

Batteries recommended are First national battery, Dixon and even Delco. With the AGM I will suggest the Omnipower.

With these batteries I would suggest getting a decent smart charger in the likes of Victron, C-tek or National luna. The great thing about these chargers are you can leave it on the battery when not in use as it will maintain the battery without overcharging it causing damage to the battery.

I hope this helps. This is just my simple opinion.



Umm just something to think about.

100ah is fine for running a trawling motor and electronics but he is only looking for occasional LED and a fish finder.

The question is how long to you expect to run on the battery?
Do you need a single strip LED on for 12 hours plus running your fish finder for 1 hour before you can recharge? The something like a 12 - 20ah battery will be more than enough.
But that also depends on your fish finder power usage/Size.

I have a 12v 12ah battery its just the size up from an alarm backup battery and I ran my small garmin fish finder for more than 5 hours plus more than 24 hours of a led light with 10 bright LEDs and the battery was still fine.

If you can try and find out what the usage is of your fish finder and LEDs then take your max time they will be in use and double that usage for the battery size.

On a 100ah battery you should be able to run a fish finder and a couple of LED lights for a week solid.


New member
Thanks to both of you for your replies. Regarding my power consumtion, the transducer uses a max of 500 watts.

I am not sure about LED's but can't imagine that draws much.


Both answers above are detailed and accurate... If you're definitely not adding a trolling motor, then you can get away with a lot fewer Ahs than 100. I had (and still do actually, but it's been repurposed as a gate opener battery) a Raylite "leisure" battery that has given me upwards of 12 years service. It's a 40 or 45 Ah (can't remember) that will give you a full day of sonar and an LED or two.

As for the transducer, 500W RMS doesn't mean that it draws 500W while running. I have yet to come across a satisfactory explanation of the calculation, but I have a feeling that it's 500W during a "ping" (so for a very brief moment) Otherwise a 100Ah battery would only give you between 1 and 2 hours. I suspect that an average 5 inch finder would probably draw between 3 and 6 watts.


New member
After some more online digging I see my fishfinder, a Lowrance Hook2 7X uses a max of 16,3 Watts. So if my high school physics remains intact, that means at max it will pull 1,36 Amps per hour. So as stated I would not need too big a battery. I guess the trick is to find the best value for money batter in Rand per Amp hour or so.

Regarding the different types, I am not too keen on a gel anymore due to their sensitive nature. But I am definitely wanting a sealed unit, unless convinced otherwised by a compelling argument. My reason behind it is just the less maintainance the better, but is it worth the cost factor as the AGM's do seem rather more pricey.

So I am now weighing up a bettery battery which requires possibly a more expensive charger, or just a flooded wet cell, which as I understand, requires less complicated charging.

So at this stage, is it just about budget once you know what size you looking for?
From my experience "sealed" and "maintainance free" batteries are exactly the same as ones you top up, except it has been glued closed so that you cannot top it up. Once you take the cover off it is exactly the same, 6 cells, rubber caps etc. With breath ports on the rubber caps so the fumes produced by the acid during discharge can vent. As far as I have experienced they evaporate just the same but last a 1/4 of the time they would normally as you CANT topup the water and you have to replace it, suiting the manufacturer.

That has been my experience anyway. I've found about half of the dead "maintainance free" batteries that I've picked up are actualy fine but nearly dry inside, top the acid/water like one would normally and they are fine..Sometimes the dry cell has burnt out and they can't be recovered, sometimes you need a smart charger that can pulse off the lead salt deposits to get a freshly wetted cell working again..anyway sorry point of the matter is get a battery that actually does not need topping up as opposed to one that does but you can't as it is "sealed". They should last a lot longer and may work out way cheaper in the long run even though twice the price in outlay. Not that I know much about them, but I do know to get a premium smart charger to look after the life of the battery also..
The battery BTW the served me on my kayak for three years for fishfinder, which only died now when I forgot it in a bucket outside that filled with rainwater, I dug that battery out of the recycling/e waste bins at a builders that someone had dumped, I got about 6 that day and 3 were perfectly fine after taking the glued cover off and topping up and putting into recovery on the smart charger. One ran a LED spotlight for me, one was a backup. They were all just dry, 3 had poked cells..So much for maintainance free LOL


Adding to the above... The "maintenance free" batteries usually just have a sticker over the filler caps. Tear the sticker off and you are able to get at the screw in plugs and top up with distilled water.


New member
Again, thannks for all the info. Most useful...

Let me ask this... which is more important initially, if budget does not allow both...

More expensive battery or more expensive charger?

From what I can understand from all your opinions is a poor charger will mess the battery up anyway...

So cheaper battery for now and a better charger is more viable? Or must I only consider being able to buy a top quality of each simultaneously?

Regarding the charger...what specs must I consider? How do I know what ampage to get? What other features should i consider?


I think that if I were in your shoes, I'd buy a medium size deep cycle (about R1400 maybe less). There are alternatives to C-Tek. Smart chargers have become a lot more common with many alternatives. I've seen them in places like Adendorff (but I doubt I'd buy one from them), rather look at a place like or At least you will get some backup from them in case of a claim.

I love my C-Tek and can attest to their warranty (I had one replaced in it's last month of it's 5 year warranty without a quibble.) but they are pricey.


New member
Which c-tek model do you have?

What you think of this two optimates?


I currently only have the 3600 C-Tek... My 7200 was redistributed a year or so back. The 3600 copes ok with my 102Ah Varta deep cycle but it's a bit close to it's max capacity. I also have a Bushpower 12A smart charger (built by Sinetech) that I use on my 200Ah battery in the house (backup power for my weekly power failures on the farm).

I believe the Optimate is a good brand, and the 3 would cope fine with a 40Ah battery. The 6 would be more than you need (but nice to have) but you could get the C-Tek MXS5 for the same price (that's the equivalent size to the old 3600).

Have a look at the Power Master range from Sinetech... I don't know what their pricing is like but the one that I have is really excellent and it was significantly cheaper than my C-Tek.


Just checked the Sinetech 12V 6A and it sells for R725 ex VAT... You will need to register on their site for pricing, but yeah... The C-tek is fairly bullet proof


Senior Member
My suggestion :
Buy ordinary charger from Current Automation in Kya sand - order pay for charger and courier . it’s made for lead acid batteries .its on R 480 or around .
Its charger for smaller batteries . Constant current constant voltage with led indication ( red charging , green fully charged )
Then just buy sealed lead acid battery 12v18-20Ah .
And you will be on a R 1000 - 1100 budget .
Forbatt , Cs3 etc
If you want good battery - it’s Panasonic 12V 20 Ah but hard to get in SA . Second best is Sonnenschein / Dryfit then comes Yuasa .
Fish finders works usually on 3% pulse width duty . So 500W will be a 15W consumption .


New member
Pretty great feedback from all.

Another option you can look into is the smaller 8ah gel batteries. Maybe even get 2 of them in parallel. It will work out little cheaper and maintains easy.

I'm a firm believer in a solid battery charger as batteries are not a cheap item to replace, but this is just my opinion. If you look after your battery you will have a happy battery for many years.

1 that has hasn't let me down is the national luna 5amp charger which comes slightly under the Ctek. Don't get me wrong, the Cteks are amazing but got a little pricey recently.

I used to run a normal 7ah gate motor battery on the kayak for the fishfinder and had no problem running it for a 3-4 hour trip. The great thing about that is it was cheap to replace and just charged it with a cheap 500mAh float/trickle charger.


New member
So I decided to take the plunge and got a Ctek MXS 5.0 charger. My boat came with just a EFB 38 ah wet cell, that was rather old and damaged. The battery has been charged in recondition mode. Hopefully it gives me a bit of time to save and buy a better battery.

But I agree that a good charger is key so you don’t mess up an expensive battery with a cheap charger. The cteks have 5 year warranty is great too.

Thanks for all the input guys.


Senior Member
I'm finding this an enjoyable thread, batteries are of course a very important consideration & cost me a small fortune every 2 to 3 years as I run my boat with 3.

So, I was not the science guru at school & misjudged things entirely when I put a 2000 watt surround sound in my Pajero with 2 x Rockford P2 subs. "No problem" said my son and fitted a No 5 Cap with a nice LED display & flashing lights. Now this sound belts out for hours on end without the engine even running, which previously only lasted 10 minutes & the battery was flatter than flat!

So, just asking, why does the boating fraternity & people in the know not market or suggest Capacitors on boats?


@FoxH... My understanding of them is this... Caps don't "supply" power in the way that a battery does. Caps can be charged up (by the battery or alternator) and have readily available power for immediate high current draw. Although they are getting better as technology move along, they won't store electricity for any reasonable length of time. They are mainly used for "peak demand" supplementation.

Let's say you have your sound system with amp rigged to your boat's house battery with the usual 2.5 or 4 wire. When you pump up some serious base heavy tunes, the current required to drive the sub woofers is too high and you get a voltage drop to your sound system. Adding capacitors at the sound system provide you with "buffer" power that will provide immediate current and smooth out the current draw from your batteries.

Adding capacitors won't make significant change to your battery's capacity.


Senior Member
I think I'm still going to install a N0 5 cap to supply my 3000lph live bait pump, that thing pulls my battery down in 30 min flat, specially when I'm running 4 x tuna in the tubes & hatch full of live mackies.

As the original poster asked for help, so do a lot of us need advice when it comes to batteries & power generation & charging. Maybe you could provide an in depth tutorial on Do's & Don'ts when it comes to batteries.

I also carry a huge mobile electronic starter on the boat, I've helped not only myself but many others at sea.

This post has been very informative for me.