New engine battery advice...

Captain Crisp

Captain Crisp

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Hi - I currently have 2 leisure batteries of the type in this image.
20220411_140905_compress24.jpg One was allowed to run down and I want to replace. The new battery will start the engine. I'm pretty ignorant about electrics... do I need to buy exactly the same battery or will I be alright with this one (which has some slightly different letters!)

Screenshot_20220411-144854_Chrome_compress94.jpg

Many thanks!
Crisp
 
Do you have 2 completely different banks and just use one battery for starting the engine and the other for services? If so, that battery will do the job, but is bigger than needed just to start the engine. If however you have an old fashioned set up where both batteries are used for both purposes through a 1,2,both switch then makes sense to have both batteries the same type and capacity. However, it is not a good idea to link an old one with a new one if you are using "both" that is charging and applying load as if they are one bank. The new and old in this case are similar but not exactly the same either.
 
This might be a good time to set up separate starter and domestic battery banks, with split charging so you wont run the starter battery down by leaving a light on. Money permitting, I'd use the old battery for starting, as it will take less of a hammering, and an old, tired battery can bring down a new one it's partnered with, and the two new ones for domestic use only. A simple way to do this is to use starter sized cable for all the battery connections, + to + on the domestics, and from one battery on to the 2 terminal on a 0-1-2-both switch. Starter battery + to terminal 1 and common to the starter solenoid connection. Take the negative of the other domestic and connect it to where the - on the starter battery connects to the engine. That way position 0 isolates the starter, 1 uses the starter battery, 2 uses the domestic bank in case the starter battery fails. and both uses both batteries.

The alternator lead goes to the starter battery, the domestic supply comes from the domestics or the 2 terminal on the switch, via a fuse. You'll also want a VSR - a voltage sensitive relay that will link both sets of batteries together, probably by joining terminals 1 and 2 together. Follow the instructions that came with it

There are lots of ways to do it, and someone will be along in a minute to explain why I'm wrong, but it's a fairly simple system that worked on my old boat for many years.
 
If you use a 1 - Both-2- Off switch, as I suspect, there is no need for batteries to have same capacity, if say 1 is alway used for starting then after running sufficiently out of harbour, 2 is used for duration of voyage until engine needed.

As others have said the engine dedicated battery could be smaller as the demand less. However if use is more random then both should have similar capacity. As others have said if both are charged simultaneously it is best if both are in fair condition, but if its simple switch over then it does not matter.

Maybe a split charging system is best and I have one on current boat, and a vcr on the van , but that is more work for a non-techy person to add, and 1 Both 2 Off has served boaters well for much of the last 60 years.
 
davidej said:
MCA on the label stands for maximum cranking amps ie the most it can supply to start your engine.

780 ought to be ample for yacht sized engines.
Click to expand...
No
It stands for "marine cranking amps "

Batteries designed for marine use may be rated at MCA instead of CCA. (Cold cranking amps) The MCA rating method measures battery output at 32F, not 0F. A battery's MCA rating will be higher than its CCA rating would
 
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VicS said:
No
It stands for "marine cranking amps "

Batteries designed for marine use may be rated at MCA instead of CCA. (Cold cranking amps) The MCA rating method measures battery output at 32F, not 0F. A battery's MCA rating will be higher than its CCA rating would
Click to expand...
Ok my bad but that is serious nitpicking. The answer is the same even if the word is wrong.
 
Captain Crisp said:
Hi - I currently have 2 leisure batteries of the type in this image.
One was allowed to run down and I want to replace. The new battery will start the engine. I'm pretty ignorant about electrics... do I need to buy exactly the same battery or will I be alright with this one (which has some slightly different letters!)
Many thanks!
Crisp
Click to expand...

One is from Yuasa's "Leisure and Marine" range. The other is from their "Marine" range
If you visit Yuasa's website you will be able to compare the descriptions, data sheets and technical specifications,

L26-80 - YBX Active Leisure and Marine - Leisure, Marine & Garden - Batteries

M26-80S - YBX Active Marine - Leisure, Marine & Garden - Batteries

The points which caught my eye were that the M26-80 is optimised for use as a starter battery, has enhanced vibration resistance. dual terminals and costs more.
 
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Slight digression.

Batteries after a guy recently worked on boat, found that the two batteries (for twin outboards) are now wired in parallel.

There is no12 volt Dual Marine Battery Switch Isolator 'One, Two or Both'

Is it correct or OK for two outboard alternators to be producing a charge and send the current to the same battery as the other engine?

Is this normal and safe practice?
 
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