Two smaller batteries cheaper and better than one large?!

[jwardmagic]

I am searching for a battery to buy for my 55lb trolling motor and am confused about two types. The Numax CXV24MF 86ah and the M135 Premium Numax Deep Cycle Marine 135ah.
The smalled ah CXV24MF battery weighs 19kg and costs ?60 with ?10 postage.
The larger ah M135 battery weights 42.5 kg and costs ?90 with ?50 postage.

Why is this? The 86ah battery has more than half the amp hours of the 135ah (135ah / 2 = 67.5ah) yet weighs less than half (19kg) AND costs a lot less?

Surely one could just connect two of these batteries, save a lot of money, save a lot of weight (2 of the smaller 86 ah batteries would total 38kg, 4.5 kg lighter than the larger battery) and at the same time get 172ah instead of 135!?

Is there a catch to this?
The weights of the batteries can be seen on the following link if you search the lists for the M135 and the CXV24MF: http://www.manbat.co.uk/cm/files/brochures/battery_specification.pdf

I hope someone can help!

 

[saildan]

Re: Two smaller batteries cheaper and better than one large?!

I am searching for a battery to buy for my 55lb trolling motor and am confused about two types. The Numax CXV24MF 86ah and the M135 Premium Numax Deep Cycle Marine 135ah.
The smalled ah CXV24MF battery weighs 19kg and costs ?60 with ?10 postage.
The larger ah M135 battery weights 42.5 kg and costs ?90 with ?50 postage.

Why is this? The 86ah battery has more than half the amp hours of the 135ah (135ah / 2 = 67.5ah) yet weighs less than half (19kg) AND costs a lot less?

Batteries have three key characteristics and a single battery can vary all three.

AMP Hours - a function of the cells, mainly surface area of the plates.

Battery AH / amp load = available runtime (some variables modify this a bit)​

Battery Life - The number of normal charge/discharge cycles the battery is built to endure. Chiefly a function of plate thickness, secondarily the electrolyte type and plate technology. However, it still comes down to the thicker the plate the longer the life, but also the heavier/larger the battery.

Type - Wet, AGM, or Gel - along with open or sealed. Equating to the maintenance and convenience level you desire.

So, in your conundrum the weight difference is comparing batteries with two different battery life levels. The AH difference points out the plate surface area variance.

Since battery companies have no control over how you discharge and charge your battery they just give a size and weight and let you equate that to battery life.

 

[pmillar]

Re: Two smaller batteries cheaper and better than one large?!

One bonus with a two battery setup is if you drain one dead (with a trolling motor for example) you still have one left to start your engine to get you home. You also have more options re. weight distribution but that could be a negative as well as a positive in finding somewhere to put a 2nd battery + wiring, depending on your boat.

 

[jwardmagic]

Re: Two smaller batteries cheaper and better than one large?!

So which would be the better setup out of the two batteries I listed? The two 86ah batteries or the one 135ah?

 

[saildan]

Re: Two smaller batteries cheaper and better than one large?!

So which would be the better setup out of the two batteries I listed? The two 86ah batteries or the one 135ah?

I believe you have become focused on Amp Hours and are overlooking the other design elements of the two batteries.

The XV24MF is a true "Marine" battery, meaning it is designed to support both the short burst, high amp demand of an engine starter (Cold Start Amps) and the slow discharge deep cycle demand of a trolling motor (Ah rating).

The M135 is Deep Cycle only, intended for running a trolling motor but NOT starting an engine.

The XV24MF weighs 19k, the M135 42.5k meaning the M135 has a longer life expectancy (more discharge/charge cycles).

Simply judging by weight as a measure of durability, the XV24MF cost is 3.16 ? / kilo, the M135 cost 2.12 ? / kilo. So, pound for ? the XV24MF is more expensive, reflecting its dual purpose design.

If you are only running the trolling motor, the XV24MF would be a waste of money, paying for a Cold Start ability you'll never use.

An apples to apples comparison would be between the M85 and the M135 or the XV24MF and the XV60 or XV70.

Post has nothing to do with battery function, of course. Perhaps a carrier like UPS or FedEx Ground would be a more economical choice for shipping heavy parcels.

 

[jwardmagic]

Re: Two smaller batteries cheaper and better than one large?!

If you are only running the trolling motor, the XV24MF would be a waste of money, paying for a Cold Start ability you'll never use.

But I'll still get a longer 'run' time by buying two of these and conecting them with my troling motor than the M135 wouldnt I? Plus it would be cheaper? Yes I'd have a cold start ability that I wouldn't use, but still, cheaper?

 

[saildan]

Re: Two smaller batteries cheaper and better than one large?!

But I'll still get a longer 'run' time by buying two of these and conecting them with my troling motor than the M135 wouldnt I? Plus it would be cheaper? Yes I'd have a cold start ability that I wouldn't use, but still, cheaper?

On the surface it appears that way. You'll need to study up on running batteries in parallel to learn if the Ah is actually doubled or if some other factor knocks some off a theoretical linear relationship. And, does the Cold Start ability deminish the Deep Cycle capacity if it goes unused.

Two other things to check on are, if one battery is rated at a 500 cycle lifespan does placing two in parallel extend that to 1000? And what will the charger requirement change to for maintaining two batteries at one time. Or, will buying two small chargers to work separately be more cost effective than buying one higher capacity charger to maintain both batteries at once?

Some good questions to put to the technical support staff at Manbat.

 

[jwardmagic]

Re: Two smaller batteries cheaper and better than one large?!

The M135 is Deep Cycle only, intended for running a trolling motor but NOT starting an engine.

Actualy both the M135 and the other are marine AND engine start batteries...it says in their specs they are both dual purpose? Im very confused

 

[TerryMSU]

Re: Two smaller batteries cheaper and better than one large?!

I am searching for a battery to buy for my 55lb trolling motor and am confused about two types. The Numax CXV24MF 86ah and the M135 Premium Numax Deep Cycle Marine 135ah.
The smalled ah CXV24MF battery weighs 19kg and costs ?60 with ?10 postage.
The larger ah M135 battery weights 42.5 kg and costs ?90 with ?50 postage.

Why is this? The 86ah battery has more than half the amp hours of the 135ah (135ah / 2 = 67.5ah) yet weighs less than half (19kg) AND costs a lot less?

Surely one could just connect two of these batteries, save a lot of money, save a lot of weight (2 of the smaller 86 ah batteries would total 38kg, 4.5 kg lighter than the larger battery) and at the same time get 172ah instead of 135!?

Is there a catch to this?
The weights of the batteries can be seen on the following link if you search the lists for the M135 and the CXV24MF: http://www.manbat.co.uk/cm/files/brochures/battery_specification.pdf

I hope someone can help!

Battery weight tells how much lead is in the battery. More lead means better mechanical strength (thus better tollerance of vibration) and also lower internal resistance thus lower internal drop. If cost and lowest weight were all that were important I would buy a pair of 9 volt transistor batteries and put then in series. . Of course we all know better than that, but I was making a point. Also, two batteries in parrallel will not share evenly, the system will be limited by the weakest of the two batteries. You will not get twice the 86AH. In series, they share much better (86AH , but twice the voltage).

TerryMSU

 

[steelespike]

Re: Two smaller batteries cheaper and better than one large?!

If your going to be running a trolling motor a true deep cycle will last longer.
The less it disscharges on each use the more cycles it can go.
And a deep cucle will start an engine fine. Cold cranking amps are listed and are adequate.And don't really apply to you as yours would be run it temperate weather.
My electric car came with 6 135 amp hour batteries in series for 72 volts.
The car could discharge them to 40% in about 1 hour yet with good care and a little luck they would last up to 3 years.
Invariably batteries in parrellel or series one or more will likely end up with less charge than the other(s) requiring individual charge or a balancing charge.
And the system will be no stronger than the weakest battery.
If you want the ultimate bang for your buck put 2 6volt golf cart batteries
in series,Dollar for dollar you can't beat them. They can be charged individually with 2 Harbor freight 12 volt 10 amp chargers.And you can leave the chargers on to maintain through the winter.All way charge your bateries as soon as possible after use.

 

[saildan]

Re: Two smaller batteries cheaper and better than one large?!

Actualy both the M135 and the other are marine AND engine start batteries...it says in their specs they are both dual purpose? Im very confused

Me too. I saw that, yet on the comparison sheet first referenced the Cold Start amps for the M135 says N/A. What gives with that Manbat