Why do I need a starter battery?

[demonboy]

I was chatting to a long-term liveaboard here (half way round the world, ten years aboard, same set of batteries and all that) and we were discussing starter batteries, or the argument for not having one.

I have four batteries, three domestic and one starter, but they are all the same (you can't get deep cycle, gel etc over here in India) yet the starter battery gets used just once: to turn the engine. Then it sits there and does nothing.

Why not have four domestic batteries instead? Maybe have a fifth that is tucked away, charged occasionally and used only in emergency for starting the engine, but otherwise just have all four as my domestic. I mean I've lost count of the times I accidentally started my engine on my domestic batteries, or weighed anchor with my starter battery.

Let's be practical here. As a liveaboard of seven years I'm finding my starter battery almost a complete waste of space. The extra power could be useful and I'm set up to keep 400aH bank charged, I have 6x40 solar panels to keep them sweet.

If I were to go down this route and had a spare battery just for an emergency, what's the smallest size required to turn an engine?

Comments appreciated, especially from those with practical experience (I'd be interested to know what your cruising scenario is). Throw the text-book out the window!

 

[macd]

If I were to go down this route and had a spare battery just for an emergency, what's the smallest size required to turn an engine?

Hi mate, how's India?
You can remember the bad old days when you used to own a car, I presume? How big was its battery? They don't need to be huge at all. Your handbook should tell what CCA (cold cranking amps) the starter needs.

 

[ChrisE]

I think that you have answered your own question, a spare battery charged occassionally, like one of those jobbies from Halfords for starting a car but how would you remember to charge it?

FWIW, I carry one of those battery packs for emergency starting and guess what? It is flat.

 

[mikegunn]

I was chatting to a long-term liveaboard here (half way round the world, ten years aboard, same set of batteries and all that) and we were discussing starter batteries, or the argument for not having one.

I have four batteries, three domestic and one starter, but they are all the same (you can't get deep cycle, gel etc over here in India) yet the starter battery gets used just once: to turn the engine. Then it sits there and does nothing.

Why not have four domestic batteries instead? Maybe have a fifth that is tucked away, charged occasionally and used only in emergency for starting the engine, but otherwise just have all four as my domestic. I mean I've lost count of the times I accidentally started my engine on my domestic batteries, or weighed anchor with my starter battery.

Let's be practical here. As a liveaboard of seven years I'm finding my starter battery almost a complete waste of space. The extra power could be useful and I'm set up to keep 400aH bank charged, I have 6x40 solar panels to keep them sweet.

If I were to go down this route and had a spare battery just for an emergency, what's the smallest size required to turn an engine?

Comments appreciated, especially from those with practical experience (I'd be interested to know what your cruising scenario is). Throw the text-book out the window!

Insurance! and cheap at that.

For the one time your anchor drags, with a rising onshore wind at 02.00 hrs, just off a rocky shoreline and you are suddenly aware that you inadvertantly depleted your only source of 'lectricity raisng and lowering the anchor a number of times a few hours earlier in an effort to get it set.

A lot of modern engine electronics won't even let you start the engine unless they can see something over 12V.

 

[vyv_cox]

I agree, and a knowledgeable USA poster has aired the same views here. My domestic bank is 3 x 110 Ah, which is sufficient for our needs. Until recently these were flooded acid leisure types that had lasted six or seven years. They were invariably used for starting the engine. They failed last year after my prolonged absence from the boat and have been replaced with Bosch sealed ones that apparently have a good reputation in this application. For the past three or four seasons my starter battery has been a small AGM type Red Flash 900, used very rarely. It has never failed to start the engine but struggles if its charge has been allowed to run low. I will buy a size bigger when it needs to be replaced. Its advantage was that I can locate it in the engine compartment, leaving the moulded in battery box for the three domestics.

Six months per year in Greece. Left in winter with a 38 watt solar panel charging all via a regulator.

 

[wytco0]

Sorry I cant give you an answer based on my cruising experience as I have none however I can add a little to the thinking behind batteries as I have a similar setup in my 4x4 expedition landrover.

For starting an engine you need a lot of amps and you want to be certain that they are available.

For general uses such as lighting, fridges, running inverter etc you want a battery that can discharge at a relatively low rate for a long period.

You do not want your general use to deplete your starter to the extent that you can't start the engine.

Starter batteries are designed to produce a lot of current for a short period of time and ideally never to be discharged very much.

Leisure or deep discharge batteries are designed to withstand lowish current draw for long period and with a high discharge capability.

They are all a compromise and each will work in each environment however like most compromises you wont get the best out of them if you don't use them as designed.

 

[wytco0]

..... Its advantage was that I can locate it in the engine compartment, leaving the moulded in battery box for the three domestics.

Thats is very important as cables waste power so keeping them short and fat (just like me) is important for starting.

 

[Tranona]

Do the same as Vyv (if you can get one). Fit a Red Flash dedicated starter battery and use all 4 of your present batteries for a house bank. If you have space you can use a normal engine start battery which is much cheaper than a Red Flash. Also fit something like a BEP Marine switch cluster with a VSR to automatically charge the engine battery first (it needs very little) and then the house batteries. Has individual isolators for each bank and a parallel switch if your starter battery fails, so you can use the house to start in an emergency.

 

[demonboy]

Starter batteries are designed to produce a lot of current for a short period of time and ideally never to be discharged very much.

Leisure or deep discharge batteries are designed to withstand lowish current draw for long period and with a high discharge capability.

They are all a compromise and each will work in each environment however like most compromises you wont get the best out of them if you don't use them as designed.

Hi wytco, I understand the differences but I did explain that here in India it's lead-acid/sealed lead acid or nothing, so I don't have that luxury of decided which does what.

FWIW, I carry one of those battery packs for emergency starting and guess what? It is flat.

Was that a factory fault or because you forgot to charge it? As a liveaboard I'm always on the case with my batteries and rarely are they left for long periods without attention.

Hey Mac, nice to hear from you! India is fantastic, though the cruising leaves a lot to be desired. Food's good though

 

[demonboy]

Also fit something like a BEP Marine switch cluster with a VSR to automatically charge the engine battery first (it needs very little) and then the house batteries.

Funnily enough I am currently installing a Sterling alternator to battery charger (Pro Alt C) which does exactly that.

 

[ChrisE]

Was that a factory fault or because you forgot to charge it? As a liveaboard I'm always on the case with my batteries and rarely are they left for long periods without attention.

I forgot to charge it. My point was when we lived aboard we, too, kept on top of the batteries but would I remember to charge a battery that wasn't attached? Sooner or later I'd forget.

The solution outlined by Vyv & co where the starting battery is automatically topped up when the engine is started has my vote.

 

[Boo2]

I have four batteries, three domestic and one starter, but they are all the same (you can't get deep cycle, gel etc over here in India) yet the starter battery gets used just once: to turn the engine. Then it sits there and does nothing.

Why not have four domestic batteries instead? Maybe have a fifth that is tucked away, charged occasionally and used only in emergency for starting the engine, but otherwise just have all four as my domestic.

Just a thought but your 5th battery sounds pretty similar to your current starter battery...

Fwiw, my intention is to have a starter battery which is continuously connected to the engine starter and alternator with a second domestic bank and join the two with a dual sense voltage-controlled relay (VSR) like this one from BEP.

The rationale for this is that the starter battery will never be much discharged by any single start so the VSR will switch on soon after each start and charge the main bank from the alternator each time the engine is run.

My long term intention is to have solar and wind chargers and these will be connected to the domestic bank hence the requirement for the VSR to be the dual sense type. I will ideally wire the domestic and starter batteries so that either (but not both) can be connected to the engine, but this is dependant on finding a suitable switch.

Hope this is of interest,

Boo2

 

[VicS]

As Vyv indicates the Americans prefer to have a large all-purpose battery bank plus a small reserve battery.

It is, I understand, what Calder describes in his book.
IIRC the domestic bank get the direct priority charging with the reserve battery being topped up via a VSR.

British preferred practice seems to be to have dedicated house and engine start batteries, with the engine start battery receiving the priority charging when a VSR is used.

Each system, IMHO, has its merits and at the end of the day its the owner's personal preference that counts.

The Sterling A to B chargers are a little different.
Both batteries are charged simultaneously, the house battery being charged in an "enhanced" mode while the starter/reserve battery receives bog standard charging as it would from a standard alternator. Their main attraction is that they are simple "add-on" units requiring no alternator modification.

 

[demonboy]

OK, thanks for the input everyone. Vyv/Vic: it's an American I was discussing this issue with.

I take your point, Chris. Easy to say you'll charge it but different in practice when it's not connected. Thanks all for the info on VSR too. I wasn't aware of these.

Boo2 - it's certainly of interest, but I'm a little confused by your explanation. You say you'll 'have a starter battery which is continuously connected to the engine starter'. Could you clarify further?

Vic, from what I understood the Sterling actually gives priority to the starter battery, not domestic, and senses which needs priority. Therefore I don't understand how this is different to a VSR. Are you saying the VSR is an either/or charging solution that only switches over to domestic after starter is fully charged?

 

[lenseman]

Hi Jamie - You don't 'need' a starter battery.

You can walk round the front of the boat, find the hole and use a starting handle like me?

 

[VicS]

Vic, from what I understood the Sterling actually gives priority to the starter battery, not domestic, and senses which needs priority. Therefore I don't understand how this is different to a VSR. Are you saying the VSR is an either/or charging solution that only switches over to domestic after starter is fully charged?

The Sterling operates in a different and more complex way . It is illustrated by a couple of graphs in the instructions.

A VSR gives total priority to one or other of the batteries... your choice which that will be .. until the volts have risen to the set value. Then it closes and both batteries are charged in parallel.

If you have dedicated starter and domestic batteries then, IMO, it makes sense for the starter battery to have the higher priority.
In the "American" system the main battery will have priority, the reserve battery only being topped up when the main battery reaches the VSR's pre-set voltage.

If the alternator has any form of smart charging or boost gizmo then with a VSR both batteries will receive the enhanced charging.
The Sterling AtoB only enhances the charging of the house or main battery. bank

 

[mikegunn]

There is another way of looking at battery management which works very well on our boat, a catamaran.

All charging sources, engine alternators, solar and generator are only connected to the service battery bank. The engine start batteries (2) are maintained by being charged from the service bank through "CTEK" 12v to 12v chargers. This means that even when at anchorage for lengthy periods, the engine start batteries will constantly be maintained in a charged condition. It is a very simple system.

 

[Tanqueray]

I also opted for the 'Two equal banks' option after having spent over a year wading through various technical stuff. I'll post more later but it came down to two very important points in the end;

1. Modern sealed AGM's (we have Rolls 1000 a/h) have massive CCA's in addition to cyclic performance when fitted in large banks.

2. It is far simpler, more efficient, and safer to set up a modern charger to charge batteries that are offload when being charged in absorption and float mode (so that the charger sees only isolated batteries not varying system load).

Two identical banks (Port & Stb'd), one bank in use at any time, bulk charge in use bank (alternator or whatever) between 50 & 80%, absorption & float charge the isolated bank to 100%.

Steve

 

[Sybaris]

There is another way of looking at battery management which works very well on our boat, a catamaran.

All charging sources, engine alternators, solar and generator are only connected to the service battery bank. The engine start batteries (2) are maintained by being charged from the service bank through "CTEK" 12v to 12v chargers. This means that even when at anchorage for lengthy periods, the engine start batteries will constantly be maintained in a charged condition. It is a very simple system.

This sounds like a great idea to me. I did a quick search on the web but cannot find any 12V to 12V CTEK charger, can you give a link.

Cheers,
Per

 

[Boo2]

Boo2 - it's certainly of interest, but I'm a little confused by your explanation. You say you'll 'have a starter battery which is continuously connected to the engine starter'. Could you clarify further?

Yes, sorry that was a bit opaque. What I meant was the starter battery will be permanently connected to the alternator and also to the ignition circuits via the normal ignition switch so it is dedicated as an engine start battery and cannot be used as a domestic / house supply battery. I obviously didn't mean it would be permanently running the engine starter motor


Boo2