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Float Tube Fishing in Ireland

Having a really great time fishing from the world's best floating fishing platform

Batteries & Chargers - Powering it up
Normally we are looking for a source of 12 volts onboard our tube. Car and motorcycles and quad riders all use lead acid batteries with a 12V rating, but these are not suitable for use. This is because the chemical inside is an acid. there are refill caps on top of the battery, and these may not be tight enough, so some day, if we have the battery on it's side, we may get a leak which burns holes in out tube, clothing and tackle. The normal lead acid battery is designed for upright storage only.
The standard answer is a sealed lead acid (SLA) 7 amp 12 volt battery. This type has no re-openable filler caps through which a leak can occur. So it is safe to use either upright, or laying on it's side. Although if you drop it, and crack the case, you will get a leak through the crack from the damage done. A 7 amp hour SLA has plenty of juice to run a sonar continuously, without worrying about running the battery down.

There is an improved version called Gel Cell batteries. These look the same as the lead acid, but the chemicals inside are in a gel form and cannot spill even if the case does crack. and ruin your equipment. They are more costly than SLAs, but last longer under use, so you get something for the extra.
Because they are cheap, and simple, and available in most places. SLAs and Gel Cells in the 7Ah size are very popular and make up 90% of all batteries in float tubes today.
So much for the advantages. What are the disadvantages of SLA and Gel Cells?
The convenience of SLA and Gel is offset to a certain extent by four things. Manage these and they will serve you well.
Think about your car for a moment. You start the engine using the lead acid battery. The battery empties somewhat doing this. Then immediately the alternator switches on to recharge the battery while you drive off.

These batteries are designed to be recharged as soon as possible after use. But we use them all day and recharge much later. This type of battery suffers from this treatment. So don't leave them for long in a discharged (empty) state, because it shortens their life substantially. Recharge with the correct trickle charger as soon as you return home, if you don't, it will age rapidly. 
Hobby shops that do model planes and camping shops sell both these batteries and chargers.
Both SLAs and Gel Cells prefer a trickle (slow) recharge. A trickle charge for this size of battery is 1/10th of the battery size. So a 7 Ah (amp hour) which is 7000 mAh (milli Amp hours) wants 700mAh recharging, and that takes 10 hours from empty. Overnight, in other words. So a quick top up charge from the car battery while you eat your lunch is not on, though a small top up may be possible.  Allow 2 hours charging for 1 hour on the water as a rule of thumb.
Don't use your car or motorcycle charger for this, it is designed to do bigger SLAs, and will be too fast/powerful for your smaller 7Ah battery. The right charger will plug in the wall, and push 500-700 mA per hour to charge your battery safely and prolong it's life. Once again, the hobby shop and camping shop sell the correct chargers.
Cold temperature reduces capacity. A SLA won't give so much power out on a cold day, and in freezing temperatures it is noticably less powerful. The only cure is to buy one larger than you seem to require, with spare capacity that is unused during summer, but will be required to keep things going during the colder weather.
SLAs  have the lowest energy density of any of the sealed rechargeables. Energy per kilo weight is low, so SLAs are HEAVY. That may be fine if the car is near to launch point, not so funny if you're carrying or backpacking tube and fishing gear to a distant water shore to launch from.
Summary for SLA and Gel Cells
Cheap, simple, handy, available, charge is simply plug in and come back tomorrow - that's why so many float tubers choose them.
The most popular size is 12V 7Ah for a full day or more.
A smaller size is the lighter 12V 4Ah size. This is suitable for a part day on the water.

Tube Sonar Power - Weighing Up Battery Alternatives

I mentioned before that I have stopped using the lead acid, and gel cell batteries to provide power for the sonar in my tube.
Here is the information I based my decision on, and some pics and details of the setup that I now use.
Now ... the battery. Although I worked my way through three of them over the years, I never liked the 7 amp hour gel cell. It is heavy enough to damage stuff if it falls, like breaking your foot if it lands on it, and it made my tube cumbersome, unbalanced and awkward to carry when loading and launching.
I wanted a lighter more compact battery than either lead-acid, or gel cell.
My sonar at the time of writing is an 
Interphase with scanning capability. It projects a narrow 12 degree beam to about 640 feet, then sweeps the beam, to draw my screen every pre-set interval, I have a 1500 watt peak to peak system here.
To find my battery power requirements I tested the sonar's power consumption. I inserted a device called a Wattmeter, in between the battery and my sonar, and this displays power being consumed. My Wattmeter shows that not everything is as you would expect in the sonar operation, and there are a few surprises.
What power the sonar really needs .....
After switching on, this sonar starts to draw power, the meter shows that it's consuming 0.4 amps, and that is 7 watts of power drain.
But does the sonar always use this power - or does it vary in its power requirement? The gain is set where I left it on my last trip, set for 15 feet deep. So what if I turn up the sonar gain to maximum, for 600 feet. Will that increase the power needs of my sonar unit?
Answer - yes.
On full gain: Power used has gone up from 0.4 amps to o.5 amps. That's only a trivial increase.
It's still burns 7 watts, and only a half amp more on full power.
If turning up the gain increased the power only a tiny bit. Then even when power is reduced no power saving occurs. Therefore the adjustment on the unit only tones down the display screen, but the transducer is on full !
Is there anything else that might increase the power demands of the sonar? How about the screen backlight?
With the backlight switched on we use more power.  Not .5 amps now, power draw rises to 0.7 amps, and total power used is now 10 watts.
So now I know the power needs of my sonar, I calculate time duration of the unit for any battery pack, with my calculater.
Let's go:
GP1300s smallest pack: 2 hrs 36 mins, or 1 hr 51 mins with backlight.

GP2200s: 4 krs 24 mins, or 3 hrs 8 mins with backlight.

GP4300s 8hrs 36 mins, or 6 hrs 8 mins with backlight.

So once I know how long I plan to fish for, I can bring the smallest and lightest pack, but still have plenty power for the sonar.
And my storage pockets are released for other necessary fishing gear.

I have three sizes of model airplane battery. All are nickel metal hydride batteries (NIMH) with a conventional steel can on each individual cell that makes up the complete battery pack. Each battery is 12V made up of 10 smaller 1.2V cells soldered together to make  a single battery pack.
I use the cheaper, steel cased, more robust NIMH type. The make of the cells are GP. I only use C or sub C cells (the fat ones) because the lighter AA cells are a bit more fragile and far slower to recharge. These C cells can be fully recharged from my car battery in 30-40 minutes from empty.
There is a newer, (more expensive) technology, called lithium polymer (LIPOLY) that a model supplier might try to sell you, but these are in a plastic covering, and can be permanently damaged by bending, puncture, or a deep drawdown, all of which happen from time to time in a tube. (Ok when protected in an appl;iance such as a mobile phone)
So LIPOLY is NOT suitable for tubing.
There might be a tiny spark when plugging the battery onto the sonar leads, so I power it off , plug the battery on, then switch on. I have never blown a fuse, but it is still in the wiring just in case.

The picture shows three packs.
The small one is GP1300s - a 1.3 amp/hour capacity.
The medium one is GP2200s - a 2.2 amp/hour capacity.
The big one is GP3300s (new version 4300) - a 3.3 amp/hour capacity.

Weight comparisons:
Gel Cell 7 ah ... 2450g / 5lbs 6 oz
GP3300s ... 600g / 1lbs 5 oz
GP2200s ... 500g / 1lbs 1 oz
GP1300s ... 200g / under 8oz

The picture shows the size, they are all a fraction of the size and weight of my previous SLA battery
The long packs are called "inline" packs, where 2 lines of batteries are soldered "nose to tail", and joined with wire at the ends.
They can be sold as "stick" packs, in some shops. It is the most common battery back shape in the hobby trade.

The smaller batteries are soldered side by side or "ladder style", and folded over to make it a bit shorter / more compact. The serious model shops will also have this shape of battery available pre-made.

The plugs are gold banana plugs, self cleaning during use, and put on in such a way as to prevent accidental plugging in with reverse polarity, something spade plugs will not prevent. The gold plate makes a good contact, so I consume lower power, and everything works better. I put a matching set onto my charger so it would connect up to the lightweight batteries.

Summary on Nimh as a Lighter Alternative
The 4.4 ah SLA is the obvious direct comparison to use. It weighs less than a 7Ah and is smaller, and once looked after I am sure would give good service.

I occasionally backpack my tube to a distant lake, sometimes climbing fences, or walking over soft boggy ground to get there, so I am happy to pay a bit extra to cut the battery weight significantly.

The three Nimh packs are ALL smaller, and ALL lighter than the 4.4Ah SLA or gel cell. it is very nice to cut more weight from a heavy fishing load, and everything still works as well as it did with the heavier gear. particularly when a lengthy walk is part of the fishing day ahead.

Nimh cost more than lead acid, and the charger costs more.

As a payback NiMh are very fast to recharge, and can be charged FROM EMPTY in as little as 30 minutes. That means a full recharge during lunch, from the cigarette lighter in the car.

What it all comes down to...always...is a combination of what we are most comfortable with and what best suits our individual styles of fishing.

Formula to calculate battery required before buying
Battery capacity x 60 / power drain = duration (in minutes)
For example ... a 7Ah gel cell :
7 x 60 / .7 = 600 minutes, which = 10 hours

Model batteries give capacity in milliamps.
So for them you must divide the result by 1000 to convert it into amps.

Like this:
GP 3600s (3600 mAh capacity) (3.6 amp capacity) made into a pack ....
3600 x 60 / 1000 x .7 (or your unit's amp draw) = 308 minutes, which is the same as 5 hours 8 mins.