House Battery Confusion ?

[businessjett]

So confused. I need new house batteries. I have no idea how big I need them to be. I would like big enough to stay at anchor for 2 or 3 days. Online says to measure all the amp draw, but I have no idea how to do that either.

My Sea Ray 275 Sundanacer has a fridge, vaculush, TV, radio, lights, water pumps, needs to charge iPhone, Mac book.

So... would anyone know roughly how much all that would draw or how big a battery I would need ? A SeaRay 275 is a 260 DA in the USA. I am in Australia.

 

[ttmott]

So confused. I need new house batteries. I have no idea how big I need them to be. I would like big enough to stay at anchor for 2 or 3 days. Online says to measure all the amp draw, but I have no idea how to do that either.

My Sea Ray 275 Sundanacer has a fridge, vaculush, TV, radio, lights, water pumps, needs to charge iPhone, Mac book.

So... would anyone know roughly how much all that would draw or how big a battery I would need ? A SeaRay 275 is a 260 DA in the USA. I am in Australia.

First, in any case, you should add a good battery monitor so you always know the state of charge. To do a load analysis like what you're talking about you will need a DC clamp meter (Fluke makes several good ones). Then measure the running loads for each item. You then need the 20 hour duty cycle of each measurement. For example the refer doesn't run all of the time - maybe 60% worst case in your area; so, then take the measurement and multiply by 0.60 and you have the load in amp hours. Now add all of that up and you'll have the 20 hour battery requirement. If you are installing lead acid batteries then you need to double the 20 hour requirement as they can only be discharged 50%. If you are installing Lithium batteries then 80%. You are going to find the battery bank is ending up quite large for a two or three day discharge duration.
Then becomes the challenge to recharge a large battery bank which I'm guessing will take between 6 and 8 hours on alternators for lead acid.

 

[Creekwood]

So confused. I need new house batteries. I have no idea how big I need them to be. I would like big enough to stay at anchor for 2 or 3 days. Online says to measure all the amp draw, but I have no idea how to do that either.

My Sea Ray 275 Sundanacer has a fridge, vaculush, TV, radio, lights, water pumps, needs to charge iPhone, Mac book.

So... would anyone know roughly how much all that would draw or how big a battery I would need ? A SeaRay 275 is a 260 DA in the USA. I am in Australia.

I have a 330DA without a generator. We anchor out for a few days at a time. I installed a pair of 6v golf cart batteries wired in series to make a high capacity 12v bank. The batteries are Rolls Surrette 6V 235 AH. The advantage of golf cart batteries is that they can be discharged much deeper without damage so you have more usable capacity. You should keep a normal group 27 cranking battery for your engine battery though.

I have replaced all my interior and courtesy light bulbs with LEDs, which reduces current draw enormously. My fridge is not the original and the new ones are better insulated, more efficient, and use quite a bit less power. I can get 3 full days at anchor and still have (barely) enough juice to start the 7.4l engine that shares the house battery bank.

 

[BarryCF]

Do yourself a favor and put in lithium (lifepo4) battery(s). If you have freezing conditions make sure the battery management system has a cold charge shutoff. They provide almost 100% of capacity Vs 50% of lead acid, can be cycled thousands (3000+) of times Vs a few hundred for lead acid.

See if you can find the documents for your current drawing devices, figure out the duty cycle, and that will tell you the amp hours capacity you need.

 

[Lazy Daze]

As a "test", I once ran 3 days and nights (same setup as you) with only ONE group 27 deep cycle battery. I did start the engine about half way through for a short run. But even on the last day, the battery still started the engine just fine.

Note... DC's shouldn't really be used for starting - I was just testing for fun.

Fridge... pack it with food. The more stuff in there, the less it has to work after the door is opened. Also, don't open the door and just stare inside the fridge like at home!

That said, there's enough room in these boats to put a Group 31 DC , which is even better... or even (2) in parallel with each other (27's or 31's). Others in this post have mentioned some good alternatives, as well.

 

[Hoplite808]

On my 270 I have a pair of standard marine deep cycle batteries as the house bank and a 1500 watt inverter that runs off of them. These are wired in as battery 2. I then have the starting battery which I also put another deep cycle, just because, and it’s wired in as battery 1. That’s what they came with from the factory. There are lots of upgrades and other stuff out there but if you want to just keep it simple just use the marine deep cycles.

 

[dtfeld]

As Tom stated, the easiest way is to install a good battery monitoring system, and it will tell you exactly how much power you are using. Monitor that for a couple of outings and you would have a very good idea. From that you can size your battery bank.

Lithium are the ideal batteries for this, but you will run into another problem. The house batteries are also the start batteries, and you can’t just drop in lithiums and call it good, without possible damage to your new very expensive lithium batteries.

A possible way to resolve this is to add a lithium “house bank”, and a DC-DC charger to access the “house battery” to keep the current batteries topped up.

Recharging also becomes and issue, you don’t say if you have a generator.

 

[Lazy Daze]

On my 270 I have a pair of standard marine deep cycle batteries as the house bank and a 1500 watt inverter that runs off of them. These are wired in as battery 2. I then have the starting battery which I also put another deep cycle, just because, and it’s wired in as battery 1. That’s what they came with from the factory. There are lots of upgrades and other stuff out there but if you want to just keep it simple just use the marine deep cycles.

Using a DC battery for starting an engine - especially a bigger one - isn't really a "bad" idea, per se. But using a dedicated starting battery is "better". It's the way the batteries are designed. All it really means, though, is that the DC being used as a starting battery won't last quite as long. Just like a starting battery being used for the house won't last as long.

FYI, your boat didn't come "that way" from the factory. Many don't know this, but the selling dealer would have been the one to install the batteries - not the factory.

 

[ttmott]

As Tom stated, the easiest way is to install a good battery monitoring system, and it will tell you exactly how much power you are using. Monitor that for a couple of outings and you would have a very good idea. From that you can size your battery bank.

Lithium are the ideal batteries for this, but you will run into another problem. The house batteries are also the start batteries, and you can’t just drop in lithiums and call it good, without possible damage to your new very expensive lithium batteries.

A possible way to resolve this is to add a lithium “house bank”, and a DC-DC charger to access the “house battery” to keep the current batteries topped up.

Recharging also becomes and issue, you don’t say if you have a generator.

And smoking the alternators. Lithium batteries are not truely "drop in".

 

[keokie]

And smoking the alternators. Lithium batteries are not truely "drop in".

I would argue lithium are the best way to go, and have become far more reasonable from a price standpoint. But as has been mentioned, they are not at all a simple drop in.

I run 2 AGM Lifeline six volts in series for 12V (the tall ones). They work exceptionally well, and I can run off them no problem and without my generator for a couple days (all incandescent bulbs, too). They will even start the motor after. Biggest disadvantage is the weight, at 94lbs each.

I will go to lithium eventually, but these are only 1.5yrs old. I replaced the last set after 9 years. They were performing fine, but I didn't want to rely on them any longer. I boat in remote areas for extended periods, and didn't want the hassle of them failing mid-trip.

 

[BarryCF]

Agree the lithium are not drop in. You need to limit the charge from the alternator. It is often done on motor homes with solar and lithium. You need to go with a Dc to DC charger. Also, the lithium batteries need to be discharged for best performance and do not like float charges. Sitting at 100% is not the best thing for lithium.

OTOH, if you have to invest in new batteries, for actual usable amp hours and life you can't beat the lithium.