Why have a dedicated starter battery?

[Mataji]

On a sailing boat with space for 2 batteries, why not have 2 leisure batteries rather than 1 leisure battery and 1 dedicated starter battery?

 

[Thistle]

So that the starting battery doesn't get flattened by all your on-board electrics.

 

[pvb]

Because people have a tendency to under-estimate their use of 12v power, and the batteries can get low on voltage, with the risk that they are unable to start the engine.

 

[PetiteFleur]

I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.

 

[Mataji]

Yes, but I can still reserve one battery for starting but use it as a leisure battery if necessary. If I use a starter battery as a leisure battery it would soon be ruined.

 

[pvb]

I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.

Not sure that is KISS, you've bought 2 batteries but are effectively only using one.

 

[CCJ]

I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.

O dear, how quaint, your gunna get some stick :excitement::very_drunk:

 

[matthewriches]

We have a customer on the river with an old hand crank Bukh, he just has an old car battery on board for his lights and a few odd things. Now that is keep it simple!

 

[peteK]

I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.

This what I have,but 2 85 amp batteries.

 

[[3889]]

We have a customer on the river with an old hand crank Bukh, he just has an old car battery on board for his lights and a few odd things. Now that is keep it simple!

No, the Pardey's did KISS. Others, like myself, sacrifice simplicity for comfort. It's not a binary scenario.

 

[maxi77]

One thing I found when I changed from using a leisure battery for engine starting to a proper starting battery was that the engine started more easily I suspect due to the battery being able to give a slightly bigger starting punch. I now have a motorhome and we dont even have a 1/2 switch, house and starter are only connected for charging

 

[BabaYaga]

Some knowledgeable people advocate not having a dedicated starting battery, but instead installing one of these:
https://www.batterybrain.co.uk/about/

 

[johnalison]

I think that KISS batteries with a 1,2/both switch is absolutely fine for simple systems, but once you have higher demands you will want a much bigger capacity, so splitting the bank into perhaps 25% for starting and the rest for service is much easier to manage and less likely to let you down.

 

[pvb]

Some knowledgeable people advocate not having a dedicated starting battery, but instead installing one of these:
https://www.batterybrain.co.uk/about/

They can't be that knowledgeable, you could spend less on a starter battery than that magic device costs!

 

[zoidberg]

I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.

That would seem to be the 'Murricain preferred way, according to guru-sparky Stu Johnson.

But.... "do NOT combine the two if one goes flat, due to a dead cell. That just pulls the good one down to 'unusable'. Instead, isolate the dead one, then switch to the good one, use that to start the engine, etc, then go home and investigate/resolve the problem."

Oh, and please don't shoot the messenger. I'm ( very ) simply reiterating a radical, perhaps heretical, approach expertly thrashed out at length elsewhere on these pages. And even cheaper, just use the sails and stick, and sail your 'fat-bottomed girl' back onto your mooring/pontoon.

Didn't they teach that on your course? Aw, diddums....!

 

[Minchsailor]

But.... "do NOT combine the two if one goes flat, due to a dead cell. That just pulls the good one down to 'unusable'. Instead, isolate the dead one, then switch to the good one, use that to start the engine, etc, then go home and investigate/resolve the problem.":

Absolutely. Never parallel a dud battery with a good one.

 

[johnalison]

Absolutely. Never parallel a dud battery with a good one.

In many years I don't think I ever paralleled mine. The only reason I can think of is if neither will start the engine in an emergency or urgent situation.

 

[wully1]

Not sure that is KISS, you've bought 2 batteries but are effectively only using one.

Only using one at a time?

Thats the system I had on my last 3 boats. My simplistic system had both batteries being charged but only one used so you always had a fully charged battery.
I never ran out of power but was ( and am) really careful with power usage.

( the only important thing I’ve run out of was gas and the lack of coffee from 7 pm for 19 excruciating hours was a well learned lesson...)

 

[Tranona]

Yes, but I can still reserve one battery for starting but use it as a leisure battery if necessary. If I use a starter battery as a leisure battery it would soon be ruined.

It depends on how complex your electricity requirements are. The requirements for an engine start battery are very different from a house bank and if you have a boat that has a high demand from the house to run hungry things like fridges and autopilots then you want as big a capacity as you can fit and have capacity to charge - dedicated to just house. On the other hand the capacity requirement for engine start is low and the current requirements high, but for very short periods, so it makes sense to have a small high CCA battery dedicated to the engine. Using a split charging system ensures the start battery is always charged and keeping the two separately switched ensures you never run the house from the start.

This is how most new boats are wired, reflecting the pattern of usage expected. However, if you have low power usage and are disciplined about keeping one of your batteries fully charged you can manage with the system you have. It is all about working out what is best for your particular situation, not being dogmatic about one way being better than another in all situations. However thew split systems are commonly used because they are probably the best solutions for most boats that have the typical modern electric and electronic gear fitted.

 

[[70521]]

I know the current thinking is to have dedicated starter and leisure batteries, but I have two 110ah leisure batteries controlled by an (old fashioned) 1 both 2 switch, so you can choose whichever for engine starting/leisure and combine the two if one goes flat. In practice I use them alternatively and have rarely had to use both. I'm a fan of the KISS principle.

Not sure that is KISS, you've bought 2 batteries but are effectively only using one.

I'll get my popcorn this is almost as good as an anchor tread.

I'm with PetiteFleure, on boats with very little power demands, and mine are falling year on year as I replace old technology with new, why have a massive battery bank? I have two 110Ah batteries with a good CCA either of them will start the 18hp engine with ease (there is also a separate 80Ah for the windlass that is never used and so is a spare). I better note that the maximum we have spent on a voyage is seven days and that was in within 150 miles of the coast.

How do two separate batteries be one apart from switching from 1 to 2 via all?

P.S. I know people who have sailed from France to South Georgia and back without a fridge or air conditioning or even a TV!