starter battery Image

starter battery

Using SmartShunt 500A with starter battery on car

Forgive me for being a novice here, but I'm trying to find an easy to install, safe Amp and volt meter to monitor the battery on my car that has an intermittent draw. I need to have something permanently installed that will give me the voltage on the battery as well as the amp draw so I can see 1) if the draw is active so I can trace it, and 2) how long I have before the battery dies. The battery is under the passenger seat, so it is basically impossible to check this with a handheld meter without taking the seat out. Thus the advantage of the bluetooth permanent install here. Can the bluetooth SmartShunt be installed on the starter battery or just a house battery on an RV, or does it even make a difference? And, it looks like I can get all the data I need from this device, am I missing something? Any help would be very much appreciated.

Ben Frobig asked
Ben Frobig commented ·

2 Answers

CYRIX-LI charge and BMV 712 settings for overcharge protection

I have a 200Ah lithium battery bank connected to my starter battery/alternator via a Cyrix-Li Charge 230A controlled by the BMV 712-Smart.

It's currently configured to only connect when the starter battery is over 14.1V (indicating that the engine is on) and to cut off when the starter drops below 13.7 (when the engine turns off). I'd like to add another condition that my lithium battery bank must be below 95% to protect against overcharging. Not having luck with the state of charge. Anyone have guidance?

Desired Logic:

ENGINE ON, BANK < 95% = Closed Circuit (aka charging)

ENGINE ON, BANK > 95% = Open Circuit (aka not charging)

ENGINE OFF, BANK < 95% = Open (aka not charging)

ENGINE OFF, BANK > 95% = Open (aka not charging)

evolutionyst asked
evolutionyst edited ·

0 Answers

Lithium Starter Battery


I've received some equipment to upgrade my boats electrical system. However the company have sent me the wrong battery (100ah drop-in lithium) - should be 100ah Victron smart.

Anyway, they are going to do a swap out, but I was thinking if it would be possible to use it as my starter battery and maybe run a few other things from it - deck wash, nav lights...

My system will have 4x 100ah Victron Lithium batteries for the house bank. This is connected to a 12/3000/120 multiplus.

The solar MPPT and Alternator are connected to a 85ah agm battery and that connects to a cyrix li-ct in order to charge the house bank when charge is available.

What I'm thinking is to do the same with the MPPT, but run it through a Battery protect and have the ignition wire for the balmar external regulator also go through a small battery protect - both will be connected to the BMS charge disconnect that I have routed through my BMV 712 relay and set to disconnect at 14.2v.

Main concern is that currently when the Cyrix disconnects when solar charge is occurring the starter gets a quick dose of around 15volts before the MPPT reduces current.

Will the BP catch this quick enough in order to stop it getting to a lithium starter battery?

I don't think the same will occur with the alternator as once the regulator ignition wire goes out the stop off current should be instant, but say if you think I'm wrong.

Hope you can clear this up and maybe give alternatives I haven't thought of.



stocksy asked
ejrossouw commented ·

1 Answer

How does the start assist on Cyrix ct? I have a problem
hello, I purchased the cyrix ct 120A relay.
I already had a similar relay from another brand, not bidirectional but unidirectional.
I installed the Cyrix as shown in the diagram: 86 chassis, 30 start battery, 87 service battery, 85 start assist, on the positive service battery with switch.
But there is a problem: acting on the start assist, the cyrix should close for 30 seconds and then open.
instead it is always closed. and the only way to open it is to disconnect the negative contact 86.
Did it arrive defective or am I doing something wrong?

buongiorno,ho acquistato il relè cyrix ct 120A.
Avevo gia un rele simile di altra marca, non bidirezionale ma monodirezionale.
L ho installato come da schema: 86 telaio, 30 start battery,87 service battery, 85 start assist sul positivo service battery con interruttore.
Ma c'è un problema: agendo sullo start assist, il cyrix dovrebbe chiudersi per 30 secondi e poi aprirsi.
invece  resta chiuso sempre. e l unico modo per aprirlo é staccare il contatto negativo 86.
Mi è arrivato difettoso oppure sbaglio qualcosa?

Francesco asked
Francesco answered ·

3 Answers

Lifepo4 house bank and AGM starter with 12/3000 multiplus

I have created 2-12.8v 300 ah LiFePo4 batteries to be wired in parallel to the Multiplus on my sailboat. I have an AGM starter battery. If I setup the charging for my LiFePo4, the float is higher than I want for the starter battery. (14.3 absorption and 13.6 float). I would like to charge the starter battery with the Multiplus. What voltages does the Multiplus use on the trickle charge output? Is it even possible to properly maintain an AGM starter battery, when the charging profile is setup for LiFePo4?

ericbjr1 asked
Justin Cook - Bay Marine Supply USA answered ·

1 Answer

Calculating Starting Battery Size

Hi All,

I have a requirement to supply 3 battery banks to start 4 engines.

Engine 1: 24VDC, 2 x 7.5kW Starters (330ah Victron AGM Battery Bank, Skylla TG 100Amp Charger)

Engine 2: 24VDC, 1 x 6kw Starter (330ah Victron AGM Battery Bank, Skylla TG 100Amp Charger)

Engine 3: 24VDC, 1 x 5.5kw Starter (165ah Victron AGM Battery Bank, Skylla TG 50Amp Charger)

Engine 4: 24VDC, 1 x 5kw Starter (90ah Victron AGM Battery Bank, Skylla TG 35Amp Charger)

I have purchased batteries to suit those recommended by the engine supplier however I need to prove that the batteries are large enough to cope with the starting currents of each engine.

Each engine needs to be able to crank for maximum of 10 seconds for 6 start attempts.

How do I calculate this?

I also need to prove the batteries can be recharged in less than 6 hours.

I calculated the charger size with the following formula:

ah of battery * 40% charger losses / charger current

Many Thanks,


MarineUK asked
ripper edited ·

1 Answer

Lithium and starter constantly in parallel when on shore power

Hi, I've recently installed a lithium bank and use a cyrix li ct to connect them for solar and alternator chargin via the starter battery. This system works great when unplugged - cyrix kicks in when there is enough solar or alternator charge and disconnects when not. However, when I'm connected to shore power and charging the lithiums with the muliplus the cyrix (rightly so) remains engaged. Just wonder if there is any damage that can be caused to either starter or lithiums doing this? If so I will just put a simple switch in the wire from the charge disconnect circuit and turn off the cyrix when on shore power.

stocksy asked
Justin Cook - Bay Marine Supply USA answered ·

1 Answer

How to install just starter batteries for a Phoenix Combi


I'd like to connect just starter batteries to my Phoenix Combi (model year ±2001). I'll use them to start the engine of my boat and while running (and the alternator as well) to feed 12V to VHF and AIS. I won't use the inverter.

Got 2 questions:

1. Do I need to connect the starter batteries to the battery connector or the trickle charge connector in this setup?
2. Do I need to also use V-sense and T-sense?


birdman asked

0 Answers

24v Multiplus: Trickle Charing a 12v Starter Battery for Generator?

I have a RV with a 24v Multiplus 3000. This is used in combination with my MPPT charger to charge my 24v house batteries.

I have a generator that uses a 12v starter battery that I would like to trickle charge using the built in Trickle charge connection on the Multiplus:


The install/user guides do not provide any information other than the Trickle charger provides 4A of current. I've measured the voltage coming out of it when I attached my Starter battery and observed current ranging from 13.5v 4A to 16v .5A.

Q1: What is the nominal voltage provided by this connection? 12v 24v?

Q2: Is there any "smart charging" provided by this trickle connection? Or is it supposed to provide a "dumb" flat charge/voltage?

Q3: If this is a 24v connection, what would you suggest for charging my 12v starter battery (there is NO alternator in my system)?

Please share your solutions! I'd love to hear what you figured out.



mikebuoy asked
GwbN answered ·

4 Answers

preset for regular car battery

I just bought the MPPT smartsolar 75/10. I am replacing an old PWM controller in an existing installation. I have a 'regular car starter battery':

Which preset should I use? This is NOT a gel battery, nor a traction battery... There is no additional information to be had from the manufacturer...


see: for details on installation

ronaldgadget asked
JohnC answered ·

1 Answer

BMS 12/200 emergency start wiring

I am building a LIFEPO4 system on my 28ft sailboat utilizing your LIFEPO4 150ah battery and your BMS 12/200. For vessel safety I must be able to start the engine using house batteries in an emergency.This could also be accomplished by some sort of start assist which is not available on the BMS 12/200. Can I just place a switched negative to the starter on the LB side of the 12/200? ofCould you please address this with a suggested wiring diagram.

Thomaskjerulff asked

0 Answers

Will a Cyrix with a charging second battery trigger start assist?

I would like to use a Cyrix-ct 12/24V 120A with a second battery that's also charged by a solar panel. The Cyrix is bidirectional, so a fully charged battery on a sunny day will also charge the first (starting) battery. Will both batteries be used if I start the engine in that situation? Will this effectively be a start assist? Obviously, I would want to do that with my AGM battery.

TurboTomNL asked
JohnC commented ·

2 Answers

Can I use a small lithium battery as a start battery?

Hi All,

Can I use one of the lithium superpacks as a start battery? What would the CCA rating be on one of them and would the integrated BMS allow it to provide the required 'pulse current' ?


Rom asked
Rom commented ·

4 Answers

How do i connect easy solar multiplus to starter battery?

Section 4.4.1 in the manual states “The Multiplus compact has a connection (+) for charging a starter battery. For connection see appendix 1”

My questions are;

Where is apppendix 1? (Not visible in appendix A)

Never mind appendix 1, where is the connection?!

All other questions on this forum seem to be advised to buy yet more victron products- a cryx - but if the manual is correct this is not necessary and is simply victron trying to sell more needless products.

If I just connect the two banks with a jump lead they will equalise, could I simply hard wire this with correctly rated cable? but is this bad practice or unsafe when using a sterling Alternator to battery charger which prioritises starter battery thus negating the priority charge process. The cryx or a cheaper simple relay would get around this, but given the functionality built in to the multiplus already I woukd like to take advantage of that. And avoids having to connect the banks.

Thanks in advance!


Will Bunce asked
Boekel commented ·

2 Answers

Fuse for Start assist on cyrix relais...

Good morning, I would like to know which fuses and cables dimensions I need for THE START ASSIST function on cyrix relais 12v 120 amper. If I got a exhausted start engine battery, a lot of current will pass through it.

Now I got four 50 amper fuses on the positives of the three batteries (1 engine and 2 services) and on cyrix..... I'm worried thei will broke, if I start engine with Start assist function.

Thank you for your answer.

Francesco asked
Hejira commented ·

1 Answer

How to monitor the starter battery with my BMV-712? Wiring seems very complicated for my installation.

0 CB_Midkiff asked · Dec 10 at 4:27 PM

I have a housebank, which is charged by a Smart Solar MMPT 100/50 and connected and supervised by a BMV-712 via shunt. In addition I have a starter battery which is not connected at all to this house system. However I would like to monitor the starter battery also via the auxiliary input of the BMV-712.

Fig. 3 of the BMV-712 wiring diagram


Issue is now that the starter battery is about 5m away from the housebank and a cable connection for high loads would be quite complicated. From the BMV-712 manual I did see that normally I would have to connect the minus of the starter battery also to the shunt via a very thick load cable and an additional thin plus cable to the B2 port of the shunt.

Is there an easier way to connect and monitor the the starter battery via BMV-712?

Would it be possible to use the Smart Battery Sense device and connect it via bluetooth with the BMV-712 as an auxiliary input for monitoring the starter battery?

Tuco asked
Redbeard commented ·

3 Answers

Temperature for house batteries and voltage for both house batteries and chassis battery

I've dug around on this board and quite find the answer. I have a BMV-712 that monitors the house batttery voltage and can also do temperature. However, if I do temperature, then I can't use the plug to monitor the chassis battery voltage.

It seems like the best solution is to use the BMV-712 for voltage on house battery and chassis battery. Now I'd be missing temperature. However, I could get a Battery Sense which transmits voltage and temperature to an MPPT controller (I have two). Since the temp is used by the MPPT controller only, this seems like a good solution. The Victron portal would show voltage from chassis and house batteries and the MPPT controllers would compensate based on temp received from the Battery sense.

Is this the only way to make it work?

sprinter2072 asked
Mark edited ·

3 Answers

Multiplus 3000 - Secondary Battery Settings?

Hi there,

I have a Multiplus 3000 230V 16A and installed it in my Motorhome. I’d like to connect the starter battery to the secondary output on the Multi. So that it can keep it topped up. I could not find any settings on this via the VE Configure software? I could see in the manual that the maximum output current is 4A but what is the maximum output voltage? Is this something that I’m able to set?

Thank you in advance

rolandka asked
rolandka commented ·

1 Answer

18 Posts
37 Users

Topic Experts

There are no topic experts for this topic. Participate in the posts in this topic to earn reputation and become an expert.