Starter battery VS. Reserve Battery

[ontherocks83]

I am sure I am splitting hairs, but I am curious as to the benefits of one set up over the other. My boat and engine are relatively small so I don't draw a lot of power on the house side or starting side. (Catalina 30 with a 21 hp Universal)

On my last boat and on the way I'm planning to set it up on my current boat is, I have a House bank and a Reserve bank. I run everything off of the house bank including starting the engine. There is an echo charger connecting the two so when the house bank is charging so is the reserve bank. My thinking is that in normal conditions I don't have to worry about switching batteries and everything is done off the House bank. If something goes wrong with the house i.e. I draw it too low or there is an internal short, I can switch to my reserve bank (1 12v battery) and start and run everything off that to hobble home. Ideally the reserve battery should always be in good shape since it will have a very easy life of only being charged and occasionally test starting the engine.

The other set up that I've had some advise to do is to use a dedicated start battery and only have the house wired to aid starting in an emergency. My concern with this (which is unlikely) is that if my House bank were low and when I go to start and my well used starter battery is bad for what ever reason, then there is no reserve to start.

Again I am sure I'm splitting hairs, but I am curious if there is a reason/benefit/whatever, to do it one way over the other that I am not aware of or am missing. Thanks

[JimsCAL]

Running everything including engine start off the house bank is what I would do. I am not a fan of start batteries as they make poor backups in case there is an issue with the house bank. I would go with a deep cycle battery for the reserve/start battery for just a bit more money.

[DefinitelyMe]

Originally Posted by JimsCAL

Running everything including engine start off the house bank is what I would do. I am not a fan of start batteries as they make poor backups in case there is an issue with the house bank. I would go with a deep cycle battery for the reserve/start battery for just a bit more money.

+1 for house bank only.

1) much cheaper and easier to buy and install an LCD voltmeter ($5 on amazon) and glance at it regularly than installing a whole setup for another battery with all it's associated paraphernalia. Not to mention the weight and storage savings from not having that battery sitting there doing nothing.

2) The problem with the setup you describe is that most 'dual chargers' work by simply paralelling the battery banks during charging, and they use the average voltage of the two banks to determine input. Since your reserve/start battery will never be discharged and your house bank may be discharged this results in chronic overcharging of the reserve/start bank and chronic undercharging of the house bank. The longevity and performance of both banks suffers.

In my opinion it's simplest, easiest and most cost-effective to have just one bank and take care of it.

[sailormed]

This is exactly the way I set up and use the batteries on our boat.

Starting is always from the house bank.

Once or twice a year I will start from the engine/reserve battery just to be sure it all still works.

[Group9]

All we have is a house bank, but we also have a generator with its own isolated starter battery. So, if we ever run the house bank down so bad we can't crank the engines, we can just start the generator, hit the pair switch (or just wait for the house bank to charge some) and we're good to go!

[john61ct]

Yes to Reserve vs Primary rather than dedicated Starters. Better redundancy, carry less "dead lead".

All sources hardwired to "Primary" aka larger House.

Kept charged with B2B if chemistry different (lead/LFP hybrid)

If voltage-following, could just be Echo Charger.

Critical load circuits, aka "Essentials": engine, safety including navigation, comms etc

segregated from "Auxiliary" non-essential loads.

Reserve sized appropriately, not usually used, but regularly tested via Cranking and Essentials easily switched over with two make-before-break 1-2 switches (no Off position). Note directing **load circuits** not charge sources, KISS.

Belt & suspenders Starting redundancy via LI jumpstarter powerpak, they make bigger ones for big diesels, fit in cargo pants pocket not shirt pocket.

Keep it charged, not used for screen gadgets, test periodically, replace every few years, use that one as a gadget powerpak.

______
Variation, for those wanting Peukert advantage of One Big Bank.

Main is made up of 12V sub "blocks", could be 6V pairs, 4 x 3v, whatever.

Put an adjustable high-ampacity LVD on one (or more) of those blocks, call that Reserve bank. Big enough for cranking and all Essentials*circuits as above.

In normal operating conditions, high SoC ranges, the closed LVD combines, full advantage of Peukert.

When Auxiliary loads start to pull voltage below your setpoint, that LVD opens, isolating Reserve subset so it is protected, always available for cranking etc.

Of course, large non-essential load circuits like entertainment should have their own LVD cutoffs set higher (earlier cutoff), refrigeration quite a bit lower (later), etc.

______

Past threads
https://forums.sailboatowners.com/th...tarter.182980/
https://www.sailnet.com/forums/gear-.../topics/298497

[guyrj33]

Originally Posted by DefinitelyMe

2) The problem with the setup you describe is that most 'dual chargers' work by simply paralleling the battery banks during charging, and they use the average voltage of the two banks to determine input. Since your reserve/start battery will never be discharged and your house bank may be discharged this results in chronic overcharging of the reserve/start bank and chronic undercharging of the house bank. The longevity and performance of both banks suffers.

In my opinion it's simplest, easiest and most cost-effective to have just one bank and take care of it.

The explanation "they use the average voltage of the two banks to determine input" doesn't sound quite right to me.

I would not go to sea without a second battery.

[Q Xopa]

Originally Posted by john61ct

Yes to Reserve vs Primary rather than dedicated Starters. Better redundancy, carry less "dead lead".

All sources hardwired to "Primary" aka larger House.

Kept charged with B2B if chemistry different (lead/LFP hybrid)

If voltage-following, could just be Echo Charger.

Critical load circuits, aka "Essentials": engine, safety including navigation, comms etc

segregated from "Auxiliary" non-essential loads.

Reserve sized appropriately, not usually used, but regularly tested via Cranking and Essentials easily switched over with two make-before-break 1-2 switches (no Off position). Note directing **load circuits** not charge sources, KISS.

Belt & suspenders Starting redundancy via LI jumpstarter powerpak, they make bigger ones for big diesels, fit in cargo pants pocket not shirt pocket.

Keep it charged, not used for screen gadgets, test periodically, replace every few years, use that one as a gadget powerpak.

______
Variation, for those wanting Peukert advantage of One Big Bank.

Main is made up of 12V sub "blocks", could be 6V pairs, 4 x 3v, whatever.

Put an adjustable high-ampacity LVD on one (or more) of those blocks, call that Reserve bank. Big enough for cranking and all Essentials*circuits as above.

In normal operating conditions, high SoC ranges, the closed LVD combines, full advantage of Peukert.

When Auxiliary loads start to pull voltage below your setpoint, that LVD opens, isolating Reserve subset so it is protected, always available for cranking etc.

Of course, large non-essential load circuits like entertainment should have their own LVD cutoffs set higher (earlier cutoff), refrigeration quite a bit lower (later), etc.

______

Past threads
https://forums.sailboatowners.com/th...tarter.182980/
https://www.sailnet.com/forums/gear-.../topics/298497

I agree with the concept. Indeed I have basicslly done mine this way.

However I'm not sure you can say 'less dead lead'. If you have a Starter or Reserve, mostly not used in my opinion it is what you are calling 'dead lead'.

If you are keeping it in 'reserve' it is 'dead lead'. If you are using it, it is not 'reserve'.

It is the same as reserve fuel, or anything.

Unless you know how use it, and for it to be in reserve. Im open to learning.

[ontherocks83]

Originally Posted by DefinitelyMe

+1 for house bank only.



2) The problem with the setup you describe is that most 'dual chargers' work by simply paralelling the battery banks during charging, and they use the average voltage of the two banks to determine input. Since your reserve/start battery will never be discharged and your house bank may be discharged this results in chronic overcharging of the reserve/start bank and chronic undercharging of the house bank. The longevity and performance of both banks suffers.

In my opinion it's simplest, easiest and most cost-effective to have just one bank and take care of it.

Maybe I should have clarified. I'm using a Xantrex Echo Charger that when it sees charging voltage at the house bank it will supply up to 15A as needed to the second bank. If the second bank is full it will only supply essentially a floating voltage and does not alter how the House bank gets charged. It does not combine the banks and outside of the selection switch on the main electrical panel I am not aware of a charger that does.

Having been stuck on the water with dead batteries and no reserve bank, I don't see it as an option at all to only rely on one bank to get me home

[Stu Jackson]

Originally Posted by ontherocks83

>>>>>>>>>>>>>>>>>>>>>>

The other set up that I've had some advise to do is to use a dedicated start battery and only have the house wired to aid starting in an emergency. My concern with this (which is unlikely) is that if my House bank were low and when I go to start and my well used starter battery is bad for what ever reason, then there is no reserve to start.

>>>>>>>>>>>>>>>>>>>>

You're not splitting hairs at all. That was a very good description.


The difficulty too many folks have is when they combine a bad and a good battery. It's an operational error.


What your setup is is exactly what I have, same engine, too!


I've been using it for 21 years. Works just fine.


Simple 1-2-B switch. Just never use B unless a charging source is present. And I don't use B 'cuz I have a combiner.


Stay with it.

[john61ct]

Originally Posted by Q Xopa

I'm not sure you can say 'less dead lead'. If you have a Starter or Reserve, mostly not used in my opinion it is what you are calling 'dead lead'.

If you are keeping it in 'reserve' it is 'dead lead'. If you are using it, it is not 'reserve'.

Well the optional setup where Reserve is just a subset of Main gives best of both worlds, but at a cost of a bit more complexity.

And even with a true set-aside Reserve, at least IMO it is much more useful "dead lead", I would not cruise without redundancy, given how essential electricity has become to increasing odds of survival.

[CFS Klopas]

The main reason I wouldn't use house for starting is I can't afford to sacrifice the MCAs. I have one start and one deep cycle FLA, using both it takes 10-30 seconds of cranking to fire my 2GM. Using a 50A "emergency" starter on shore power helps quite a bit.

[noelex 77]

The combination of dedicated house and start battery is a tried and true formula that works well.

The drawback of a house and reserve battery bank is that if the reserve battery has degraded, perhaps from old age age, self discharge or a defective charge system, this defect may not be obvious until the reserve bank is required in earnest.

Unfortunately, battery voltage is not a guarantee of battery health. The reserve battery bank can have an acceptable voltage without being capable of supplying the necessary cranking current. Thus the reserve battery bank may be defective and this failing may not be obvious until it is needed.

[john61ct]

Which is why regular live testing by cranking off Reserve is specified, even better fully cycling the Essentials circuits, watching the SoC/Ah totalizer, etc. Could be a biweekly or monthly checklist routine.

And ideally regular full load testing, more important for House as well as it is aging faster.

People that fail to properly test / monitor their batteries to prevent surprises, will get surprises, no matter the system design.

With three separate sources for cranking, odds are **better** you won't be stranded, unless you've been completely ignoring things for many months at a time.

Even with one House and one Starter, really the only difference is the secondary can help with more in providing redundancy, rather than an unnecessarily IMO rigid "Chinese firewall".

[Dockhead]

Originally Posted by john61ct

Of course, large non-essential load circuits like entertainment should have their own LVD cutoffs set higher (earlier cutoff), refrigeration quite a bit lower (later), etc.

You say "of course", but in a lifetime of cruising I've never in my life seen a lead-acid bank on a cruising boat with low voltage cutoffs, which is a concept developed in connection with lithium batteries.


I think it's a very good idea, but it's not simple or cheap to implement, and it is extremely unusual.


I don't -- of course! -- have any such devices on my boat, but I have three completely and totally separated battery banks -- house, engine start, genset start. The engine start batt does not power any thing whatsoever except the starter, and has its own separate alternator and its own separate shore power charger. It can't be drained by an operational mistake with the house batts or any fault in that system whatsoever.



If that were to ever crap out, I have a set of jumper cables, and I would jump from any one of the other 9 12v batteries I have on board. Only ever did it once in 10 years.


I will disagree with other posters and say that a separate dedicated start battery is a very good thing. Don't think of it as wasted capacity -- start batts don't have usable deep cycle capacity anyway. Think of it as -- well -- how you start your engine. The more completely separated from everything else, the better. Dual alternators on the main engine is a very, very good thing.