Charging engine battery

[MikeH99]

I wonder if anybody else has come across this. I am sitting in Majorca on our new(to us) Bavaria C42 2021 awaiting our engine battery to take enough charge to start the engine. Our guy here says that on this boat and some other new models even such as X boats, shore power does not charge the starter battery. This seems colossally stupid but he thinks it is done to save cost and has fitted a workaround solution to several boats. He is very competent and honest so I’ve no reason to doubt him. He either fits a charger that charges the engine and generator battery from shore power or a switch that allows the service batteries to supplement the engine battery.
Anyone else seen this or has comments?

 

[MikeH99]

I wonder if anybody else has come across this. I am sitting in Majorca on our new(to us) Bavaria C42 2021 awaiting our engine battery to take enough charge to start the engine. Our guy here says that on this boat and some other new models even such as X boats, shore power does not charge the starter battery. This seems colossally stupid but he thinks it is done to save cost and has fitted a workaround solution to several boats. He is very competent and honest so I’ve no reason to doubt him. He either fits a charger that charges the engine and generator battery from shore power or a switch that allows the service batteries to supplement the engine battery.
Anyone else seen this or has comments?

Should add the engine battery is near death so that will be replaced tomorrow

 

[simonfraser]

first charge the engine battery
fit a B2B, victron, or similar, or VSR to take the excess to house batteries when engine battery is full
or

 

[PaulRainbow]

I wonder if anybody else has come across this. I am sitting in Majorca on our new(to us) Bavaria C42 2021 awaiting our engine battery to take enough charge to start the engine. Our guy here says that on this boat and some other new models even such as X boats, shore power does not charge the starter battery. This seems colossally stupid but he thinks it is done to save cost and has fitted a workaround solution to several boats. He is very competent and honest so I’ve no reason to doubt him. He either fits a charger that charges the engine and generator battery from shore power or a switch that allows the service batteries to supplement the engine battery.
Anyone else seen this or has comments?

I've seen all sorts of odd wiring, including from the factory.

I would fit a VSR to charge the engine battery. I would also fit an emergency parallel switch between the engine and domestic isolator load terminals, for emergency start from the domestic batteries.

 

[Sandy]

As @simonfraser and @PaulRainbow have said, a bit odd.

While my shore power and solar is connected to the house bank once the voltage gets up to 13.8 the VSR kicks in and tops up the engine battery. The thinking is; that the engine has been recharged by the time I get back on the mooring or wriggled my way into a marina and that all 30 amps can fill the house bank until the system comes off bulk charge.

 

[Stemar]

I've always set things up so the engine battery gets charged first, because I really want to be able to start the donk, but I can live with dim lights if I have to. In practice, I never do, because the engine battery is rarely low. 100 amps for 20 seconds (it never takes that long) is about half an amp hour if my calculations are correct, or about 1% of the battery's capacity. This may be why a charging system designed by a non-sailor with an accountant on their back may think not charging the engine battery from mains is a good idea.

A way to start from the domestic bank is still useful insurance, though I only used it twice in 20 years. Batteries do fail, as do alternators.

 

[B27]

I've always set things up so the engine battery gets charged first, because I really want to be able to start the donk, but I can live with dim lights if I have to. In practice, I never do, because the engine battery is rarely low. 100 amps for 20 seconds (it never takes that long) is about half an amp hour if my calculations are correct, or about 1% of the battery's capacity. This may be why a charging system designed by a non-sailor with an accountant on their back may think not charging the engine battery from mains is a good idea.

A way to start from the domestic bank is still useful insurance, though I only used it twice in 20 years. Batteries do fail, as do alternators.

This shows that engine batteries don't need much charging.
It suggests they are prone to being overcharged if they are VSR'd to the domestic batteries all the time.
The domestic batteries want 14.4V while they are taking charge, the engine battery should be floating at 13.6 after an hour.
Maybe some boat manufacturers have been seeing premature starter battery failure?
A small solar panel should be plenty to keep the engine battery topped up through periods of non-use.

 

[PaulRainbow]

This shows that engine batteries don't need much charging.
It suggests they are prone to being overcharged if they are VSR'd to the domestic batteries all the time.
The domestic batteries want 14.4V while they are taking charge, the engine battery should be floating at 13.6 after an hour.
Maybe some boat manufacturers have been seeing premature starter battery failure?
A small solar panel should be plenty to keep the engine battery topped up through periods of non-use.

There are countless boats out there with VSRs and we don't see countless engine battery failures. I have fitted scores of them and i very rarely have to change engine batteries.

Same applies to the countless boats with mains chargers that charge engine and domestic batteries. They mostly charge all batteries on the same regime, same as a VSR will. Again, we don't see countless engine battery failures.

Of course, there are a few installations where a VSR isn't the best solution.

 

[Tranona]

I wonder if anybody else has come across this. I am sitting in Majorca on our new(to us) Bavaria C42 2021 awaiting our engine battery to take enough charge to start the engine. Our guy here says that on this boat and some other new models even such as X boats, shore power does not charge the starter battery. This seems colossally stupid but he thinks it is done to save cost and has fitted a workaround solution to several boats. He is very competent and honest so I’ve no reason to doubt him. He either fits a charger that charges the engine and generator battery from shore power or a switch that allows the service batteries to supplement the engine battery.
Anyone else seen this or has comments?

The emergency parallel switch is definitely worth fitting. Normally engine batteries get an easy life as they are charged from the engine via a splitter so fully charged with just a short period running after start. Surprised the battery has failed so quickly as Bavaria usually overspecify the engine battery for commonality with the house batteries. All 5 batteries on my 2015 Bavaria were the same Exide 95Ah AGMs and were still fine when I sold it at 6 years old. I don't recall whether the mains charger (a Cristec 40A) did the engine start, but certainly did the house and the bow batteries.

If fitting the parallel switch I would not bother with an additional mains charger - same for the generator.

 

[Buck Turgidson]

This shows that engine batteries don't need much charging.
It suggests they are prone to being overcharged if they are VSR'd to the domestic batteries all the time.
The domestic batteries want 14.4V while they are taking charge, the engine battery should be floating at 13.6 after an hour.
Maybe some boat manufacturers have been seeing premature starter battery failure?
A small solar panel should be plenty to keep the engine battery topped up through periods of non-use.

But you have to consider that once the two batteries are paralleled by the VSR the start battery may well discharge into the house until they both have the same tension so you won't be overcharging anything. The idea that one battery charges and then stays in that state when the two are paralleled is not correct.

 

[bedouin]

I can understand why manufacturers take that approach. In everyday usage there is very little power drained from the engine start battery and it will normally be adequately recharged from the alternator when the engine is running. Fitting a smart mains charger to charge two banks independently is going to be a lot more expensive and in most cases unnecessary.

A switch to parallel up both batteries to start the engine (or run essential electronics) is a very good idea and with that, should the engine battery be low you can use the domestic to help start it.

 

[Daverw]

Just had the same issue this weekend, luckily fellow boater had one of those battery packs, worked perfectly. At least I know why it was low, I’ve just replaced FET battery splitter for B2B and forgot to fit the starter trickle charge wire from the Multiplus when removing FET splitter and had been playing with it to set up and discharged the battery, 5 mins to add a ring terminal and all sorted.

Just also got out of boxes of stuff a battery switch and some cable to add emergency parallel switch which I should have done anyway

 

[William_H]

I wonder if anybody else has come across this. I am sitting in Majorca on our new(to us) Bavaria C42 2021 awaiting our engine battery to take enough charge to start the engine. Our guy here says that on this boat and some other new models even such as X boats, shore power does not charge the starter battery. This seems colossally stupid but he thinks it is done to save cost and has fitted a workaround solution to several boats. He is very competent and honest so I’ve no reason to doubt him. He either fits a charger that charges the engine and generator battery from shore power or a switch that allows the service batteries to supplement the engine battery.
Anyone else seen this or has comments?

I think it highly desirable for any owner to fully understand the charging arrangements for batteries even in a new from the builder boat. If manufacturers are puting out boats with no external charge provision for engine battery then owner should be aware. I would say a way of paralleling batteries for emergency start is highly desirable. This could also be used to charge engine battery in parallel with house batteries from external charge source. ol'will

 

[RupertW]

I’m happy with a VSR that starts charging the domestic batteries from the alternator when the voltage is high enough and have only the engine charge the engine battery - not shore and not solar. I find engine batteries work almost forever with this setup. For example we inherited an engine battery with the boat in 2010. In 2021 the boat had been completely unattended and uncharged for 11 months. The domestic batteries were 8 years old then and toast, partly because I’d left the bilge pump on them and the float switch had eventually failed on, but the engine battery still started the engine first time.

 

[simonfraser]

'A switch to parallel up both batteries to start the engine (or run essential electronics) is a very good idea and with that, should the engine battery be low you can use the domestic to help start it.'

switch over one better as the low battery then does not pull the charged one down

Paul can no doubt supply a handy diagram

 

[Supertramp]

I have experienced a flat engine battery, and alternator failure, all dealt with without excess drama due to simple flexible systems. An emergency switch joining the systems is essential. My shorepower charger normally charges the two service batteries but I can choose to charge the engine battery together or separately - useful to give the engine battery a full float charge every few months. My solar charges only the service batteries and I have an emergency start pack to back up starting the engine.

Not hard to install, clear labelling switches and wires helps, and avoids dependence on pieces of electronics which I don't understand, at least in terms of how they operate.

 

[Mudisox]

This shows that engine batteries don't need much charging.
It suggests they are prone to being overcharged if they are VSR'd to the domestic batteries all the time.
The domestic batteries want 14.4V while they are taking charge, the engine battery should be floating at 13.6 after an hour.
Maybe some boat manufacturers have been seeing premature starter battery failure?
A small solar panel should be plenty to keep the engine battery topped up through periods of non-use.

I have 3 small solar panels [ each approx 1sq foot] installed back in 1988 and still keep all my batteries both service and starting in both hulls up to scratch, throughout the year. 12.8v.

 

[madabouttheboat]

My personal choice setup would be to have en engine battery with a 1 way VSR to also charge the domestic bank when the engine is running. A mains powered battery charger connected just to the domestic bank and an emergency parallel switch to allow the domestics to start the engine if the engine battery went flat for any reason. I have rarely ever seen the need to charge the engine start battery from a mains battery charger unless the boat gets left unused for very extended periods.

 

[Stemar]

I have rarely ever seen the need to charge the engine start battery from a mains battery charger unless the boat gets left unused for very extended periods.

This is where a small solar panel comes in handy, though I'd always suggest fitting as much solar as space and budget allow. There's something very smug satisfying about sitting at anchor with ice for the G&T and the rosé nice and cool, knowing that in spite of the fridge's best efforts, the batteries are staying full.

 

[PaulRainbow]

It's important to connect the Emergency Parallel switch to the load side of the isolator switches.

1) Engine battery not quite up to starting the engine; turn the EP switch on, start the engine, turn the EP switch off.

2) Engine battery failed; turn the engine battery isolator off and the EP switch on. The engine starts from the domestic bank and can continue to run from there until you can get a replacement battery.

3) A domestic battery has failed; turn the domestic battery isolator off and the EP switch on. The domestic systems will operate from the engine battery until you can get a replacement battery.

The following schematic shows how the switches are wired (amongst other things), including a VSR.



For those who have said they would prefer a one way VSR, so the engine battery does not get charged by solar, mains etc, but the alternator charges the domestics, a VSR isn't really the answer. A better solution would be something like a Victron Argofet, as illustrated here: