Do I really need a separate starter battery

[iabmatos]

Once upon a time, someone in this forum wrote something like:

"BEWARE when combining batteries at different voltage levels!!!!! Potential for huge amount of Amps travelling instantly from the charged side to the discharged side. Ensure similar voltage on both sides or use a power resistor until no significant voltage difference measured between batteries."

Cheers

[Morequestions]

How much do they cost compared to a wet cell starter battery? I don't think any batteries are cheap these days, why take a chance ruining some high dollar battery's when you can get 4 years or so on a bottom dollar starter battery?

[goboatingnow]

People make this complex but it isn’t

If you are going down the road of the expense of lithium domestic batteries. You should focus all your charging sources to recharge your domestic systems. This is the system that will be recharged daily.

Whether you start from your lithium, have a separate lithium start battery , have a separate FLA battery etc is simply a matter of personal choice. Rig up a charging system from the domestic to charge the “ starter battery “ this could be an invertor and battery charger ( for a stand alone lithium starter pack ) , a dc dc charger for a fixed starter battery ( lithium or FLA) and so forth.

The key is to have an alternative stater system available but which exact type is rather a matter of simple personal preference.

Note that alternator failure these days is less of a concern as most people have either solar PV or a generator.

[merrydolphin]

Can you do it? Sure.
Is it ideal or preferred or “PROPER” no! I would always have a separate battery. It’s no big deal. Start batteries are much cheaper and smaller than house banks. Just a quick burst of amps and its done it’s job. All in a couple of seconds. Charges quickly too. (You have hardly used it.)

[trapoc]

I just hand crank the little diesel and yoohoo running again, skip the solo starter battery.

[Pete the Cat]

I am a old guy who got rid of my starting battery 30 years ago. I have cruised almost all of the North and Central American coasts in that time and never been sorry I did not have a starting battery. I use golf cart batteries and get 6 years or more out of them in two banks. I once ran both banks down because I had a bad cell in one bank (I run them together most of the time and never take the whole thing below 50%). I was in El Salvador so my options were limited. I turned off the switch and waited 12 hours and the good bank came back with enough voltage to start the engine. Maybe with some of the exotic new batteries that would not work, but I will never complicate my system when something simple works. I was told lead acid batteries without a shorted cell will come back with enough voltage to start a small diesel and in this case it worked fine. I do not know if it would work for everyone, but I like simple. I would rather sail than work on stuff.

[donradcliffe]

When I look at the detailed specs on lithium BMS, most of them are capable of peak starting currents of at least twice their rated amperage. If I used drop in lithiums, I would want two independent batteries rated at 100 amps discharge if I wanted to depend on them for starting.

[M-and-L]

I have pocket trawler (Nimble Vagabond) with 25hp outboard. 100ah lithium house battery will not crank the engine. Us LA start battery with Perko switch. I have noticed that they are now making lithium batteries which also work for cranking.

[lewisa]

I have used a single bank of Trojan T-105's for both starting and house for several years. I usually carried a Size 24 starting battery, but never used it; now I carry a small lithium "jump start" battery just in case. I have tested it several times and it always starts my Perkins 4-108. I rarely use more thas about 50 AH of my 225 AH house bank before recharging.

[Pete the Cat]

Originally Posted by iabmatos

Once upon a time, someone in this forum wrote something like:

"BEWARE when combining batteries at different voltage levels!!!!! Potential for huge amount of Amps travelling instantly from the charged side to the discharged side. Ensure similar voltage on both sides or use a power resistor until no significant voltage difference measured between batteries."

Cheers

Yes. That is what a battery bank switch is for. I am continually shocked at how sailors seem to enjoy complicating their lives with complexity. But I guess it keeps the economy going.

[Bowdrie]

Originally Posted by lewisa

I have used a single bank of Trojan T-105's for both starting and house for several years. I usually carried a Size 24 starting battery, but never used it;

A friend with a, (ahem, cough, cough,) power boat uses a #24 to start the "Jimmy" diesel, it's not a huge engine, perhaps 100 hp., but that single batt has no problems firing that engine.
Acknowledging the differences between gas and diesel, I remember from an engine forum that in terms of "Watt Hours", starting a 350 Chevy small block consumed less power than what is stored in an AA dry cell batt.

[rslifkin]

Originally Posted by Bowdrie

A friend with a, (ahem, cough, cough,) power boat uses a #24 to start the "Jimmy" diesel, it's not a huge engine, perhaps 100 hp., but that single batt has no problems firing that engine.
Acknowledging the differences between gas and diesel, I remember from an engine forum that in terms of "Watt Hours", starting a 350 Chevy small block consumed less power than what is stored in an AA dry cell batt.

If the engine fires with a fairly short cranking time, the total power required to get it started isn't all that much. However, you have to be able to deliver a large amount of power for a second or 2 to crank it fast enough to start.

On my powerboat, the Chevy 454 big blocks each start from a single group 27 battery and they're more than enough even under worst-case conditions.

[Shaneesprit]

The house bank battery and the starting battery are completely different although might look similar to the (insert non offensive words ) in that they are both house in plastic with 2 terminals - that’s about where the similarity ends.
The CCA delivery of a cranking battery is completely different, as you have 1200W of solar you are obviously reliant on the house bank,
Cranking batteries are high output and designed to be kept at 100% charge - the house bank completely different.

[sailingharry]

Originally Posted by Shaneesprit

The house bank battery and the starting battery are completely different although might look similar to the (insert non offensive words ) in that they are both house in plastic with 2 terminals - that’s about where the similarity ends.
The CCA delivery of a cranking battery is completely different, as you have 1200W of solar you are obviously reliant on the house bank,
Cranking batteries are high output and designed to be kept at 100% charge - the house bank completely different.

That is a technically accurate statement that doesn't apply in the real world.

Indeed, start batteries (AKA, car batteries) are optimized to get the highest possible cranking power in the smallest battery, with little regard to duration of load (but they do address "reserve capacity" or some such). So they are designed with lots of very thin plates -- lots of surface area, limited thickness for sustained current.



And deep cycle batteries, size for size, are optimized for limited draw, but for long periods of time. They have thick plates, and few of them.


However, most sailboats these days have BIG house banks, at least compared to the appropriate start battery. My boat has an 800Ah AGM bank. Each of the 4 batteries has a CCA of 1250A (I know, it's unusual for a deep cycle battery to also have a CCA rating) for a bank CCA of 5000A. An Interstate Group 24 has a CCA of 750A. So on my boat, my house bank has more than 6 times the CCA of a start battery. Even one of the batteries (a mere 200Ah), at 1250 CCA, can crank better than most start batteries.


Even my little Sabre 34, with an old 27HP Volvo, had a 220Ah house bank (two Trojan T-105 golf cart). While the difference between "deep cycle" and "cranking" batteries is real, for the large majority of sailboats, the house bank has more CCA than the start bank.

[skenn_ie]

Unless you have a pull or hand-crank start on something that can charge your batteries, you are asking for trouble. It is only a matter of time before SOMETHING discharges one bank. Life gets difficult and, if you are at sea, dangerous, without electrical power. Solar is good, wind is good, but either/both can be useless at times, and take time to recharge