2nd Leisure Battery Required - Budget Recommendations

jo10000_6

jo10000_6

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Hymer B544 Classic
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Jan 2018
Hi All,

I'm currently doing the exercise on what amps my electrical 12V bits power usage is and on paper its 3 days use from the one I have.

In practice its not turning out like that and I will no doubt post my queries when the experiment has finished.

I'd like to have a second back up battery - don't need to wire it in - I will just swop in if it is needed when I'm away with no EHU.

I considered a used battery - but then thought perhaps a budget battery (Knowing its a back up) would be better - at least I know it started off new and that I can also keep it maintained with my smart charger.

Tanya have got a Powerline cheap thing 82 ah (c20) 90 A (c100) at just under £66 delivered

Any recommendations appreciated.

Thanks Jo
 
Thanks - I know that’s correct Pappajohn - but at the moment it’s an exercise I need to run to determine what my power needs are with the back up as a spare.

I’m confident of keeping both batteries tip top.

Thanks Jo .

Ps -
My 3 Amp 12 TV is drinking lots -
When I finish do the tests - I look forward to your comments because what it seems to be doing is
driving me crazy !
 
Hi Joe,

You could always do what I've done recently and add a standalone battery which is allocated just for the TV (a 3Ah unit just like yours).

I have two new Yuasa L36-EFBs connected to the hab system and a single Varta 95Ah AGM which just supports the TV.

We have a compressor fridge and, since I had a spare AGM battery, I thought I would use it wisely. My battery @30% DOD has 66.5Ah available (give or take) so that gives a huge amount of telly hours before I need to recharge the standalone battery.

It works for us but others will have different ideas.

Good luck,

Andrew
 
Always remember your battery capacity is lower the higher your load is. Also unless you can measure the electrolyte density voltage is a very poor measure of remaining capacity unless you can disconnect the battery for several hours to let it stabilise. Voltage whilst on load is always lower than 'real' voltage

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What's size/type/model is your existing battery?
 
How are you monitoring usage?
I'd suggest getting a battery monitor to understand Watts really going in and out.
If you're simply waiting until the battery has reached a particular Voltage, how will you know what capacity it had?
Any results will be interesting.
I've tried having stand-by batteries. Killed every one. Maybe you can look after them better than I did but I don't think it's worth the faff.
 
Blue Knight said:
Hi Joe,

You could always do what I've done recently and add a standalone battery which is allocated just for the TV (a 3Ah unit just like yours).

I have two new Yuasa L36-EFBs connected to the hab system and a single Varta 95Ah AGM which just supports the TV.

We have a compressor fridge and, since I had a spare AGM battery, I thought I would use it wisely. My battery @30% DOD has 66.5Ah available (give or take) so that gives a huge amount of telly hours before I need to recharge the standalone battery.

It works for us but others will have different ideas.

Good luck,

Andrew
Click to expand...



Hi Andrew - this may need to be what I do …..we don't watch a lot of TV but its nice on an evening just to settle to a film.
Thanks Jo
 
maxi77 said:
Always remember your battery capacity is lower the higher your load is. Also unless you can measure the electrolyte density voltage is a very poor measure of remaining capacity unless you can disconnect the battery for several hours to let it stabilise. Voltage whilst on load is always lower than 'real' voltage
Click to expand...


Ohhhhhh - I may have been measuring wrong …….but still sounds like I'm using a lot - I'm posting later on my "issue" - I've been measuring as I'm going through the tests and at the end. (n)
 
two said:
How are you monitoring usage?
I'd suggest getting a battery monitor to understand Watts really going in and out.
If you're simply waiting until the battery has reached a particular Voltage, how will you know what capacity it had?
Any results will be interesting.
I've tried having stand-by batteries. Killed every one. Maybe you can look after them better than I did but I don't think it's worth the faff.
Click to expand...


I'd like a battery monitor and have had some recommendations. I'm thinking I may have gone about this is a very "black and white" way ! But I like and white and dislike grey ! Grey makes my head hurt. The truth is I actually like to understand things and when I don't it nags me.

I also have to say …..I do like to faff.

The law of diminishing return applies to me lots but I cant seem to switch it off. :whistle:

I shall post my results that may now have been taken naively.
 
You cannot manage what you cannot measure.
At least you are trying to measure.
Post your findings when you have them.
I'm sure that the forum be happy to draw conclusions.
 
jo10000_6 said:
Hello Minxy girl - its a 110 Amp Exide ER550 - approx. 10 months old.
Click to expand...
If you do find you need another, I'd stick to the same size if it will fit alongside the existing one, if your wallet will allow getting the same make/model too, this should then give you spare capacity in the system so you never badly discharge them, however you need accurate details of your needs to make your final decision.
 
The problem with measuring battery voltage is that, although you can measure the voltage accurately to the nearest 1/100th of a volt, it is not an accurate measure of the state of charge of the battery.

Tests have shown that the 'resting voltage' is a reasonably accurate way of measuring state of charge. Resting voltage is measured when the battery has been disconnected from any loads or chargers, and has been 'resting' for a few hours.

Measuring the battery voltage while under load is kind of useful as a guesstimate, but is mostly very misleading.

As @max177 says, measuring the specific gravity of the electrolyte fluid is an accurate way to measure the state of charge, but is usually impossible with sealed batteries, and gel/agm which don't even have a liquid electrolyte.

You can use a battery monitor, which has an inbuilt computer that continuously measures the amps going in and out of the battery, and keeps a count of the amp-hours of charge. The display can be set to show the percentage state of charge. It is accurate even when the battery is under load or is charging.

Without a battery monitor, you can measure the resting voltage by disconnecting all loads and chargers (including solar) and letting the battery stand for an hour or two. Accurate but tedious.
 
autorouter said:
The problem with measuring battery voltage is that, although you can measure the voltage accurately to the nearest 1/100th of a volt, it is not an accurate measure of the state of charge of the battery.

Tests have shown that the 'resting voltage' is a reasonably accurate way of measuring state of charge. Resting voltage is measured when the battery has been disconnected from any loads or chargers, and has been 'resting' for a few hours.

Measuring the battery voltage while under load is kind of useful as a guesstimate, but is mostly very misleading.

As @max177 says, measuring the specific gravity of the electrolyte fluid is an accurate way to measure the state of charge, but is usually impossible with sealed batteries, and gel/agm which don't even have a liquid electrolyte.

You can use a battery monitor, which has an inbuilt computer that continuously measures the amps going in and out of the battery, and keeps a count of the amp-hours of charge. The display can be set to show the percentage state of charge. It is accurate even when the battery is under load or is charging.

Without a battery monitor, you can measure the resting voltage by disconnecting all loads and chargers (including solar) and letting the battery stand for an hour or two. Accurate but tedious.
Click to expand...




I may have been prematurely measuring then - didn't wait an hour or two to be fair - however the loads were not huge and so would this have a bearing on how accurate the measurements may have been ? (2 and 3 amp respectively). ?

Thanks
Jo

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The answer is I don't know. It depends on many things, including how deteriorated your battery is. But it's easy to check - take a measurement just like you did already, then disconnect the battery, wait an hour or two and measure again.

The big problem is that a tiny voltage fluctuation of 1/10 volt is very significant when looking up the state of charge in a table of voltages.
 
autorouter said:
You can use a battery monitor, which has an inbuilt computer that continuously measures the amps going in and out of the battery, and keeps a count of the amp-hours of charge. The display can be set to show the percentage state of charge. It is accurate even when the battery is under load or is charging.
Click to expand...
I've got the ones that you can read the state of charge on at that particular point in time, but as you say their accuracy isn't great, so having a way to do it more accurately would be great.

Is there a particular battery monitor you'd recommend in order to get an accurate reading (using the method stated above) that can be easily retrofitted and doesn't cost and arm and a leg?
 
Minxy Girl said:
Is there a particular battery monitor you'd recommend in order to get an accurate reading (using the method stated above) that can be easily retrofitted and doesn't cost and arm and a leg?
Click to expand...
I use the one built into the Electroblock, which is OK for me because I'm only interested in the batteries connected through the EBL, and I don't have solar (yet).

Other people recommend the NASA BM types or the Victron BMV types. These have a 'shunt' that you wire into the negative lead next to the battery terminal. They are more expensive than the simple volt/ammeter types.

It seems to me there's no good reason that a clamp sensor isn't used for the amps measurement instead of a shunt. It would simply clip around the wire. However I don't know of any battery monitor that uses a clamp instead of a shunt.

Silicon chips that perform all the measurements and calculations are easily available, so it wouldn't surprise me if there were cheap Chinese battery monitors on the internet. The hard bit would be trying to find out if they do the measurements and calculations, and not just measure the volts and amps.
 
autorouter said:
It seems to me there's no good reason that a clamp sensor isn't used for the amps measurement instead of a shunt. It would simply clip around the wire. However I don't know of any battery monitor that uses a clamp instead of a shunt.
Click to expand...
I think the reason for this is that clamp measurements of DC are affected by the ambient magnetic field in the vicinity. I have a multimeter with DC clamp current measurement built in and there is a need to press the 'cal' button with the clamp in the same orientation as it will be when measuring, to zero it in the magnetic field, then place it round the wire and carry out the measurement of current in the wire. This process wouldn't be practical for continuous measurements using a permanently fitted clamp sensor, unless it also had a reference sensor beside it, I suppose. Even then, I expect it wouldn't be as accurate as a shunt. It would be a good little project for someone with the programming knowledge and a bit of time on their hands to test it out.
 
As I understand it a lot of the cheaper leisure batteries are just re labelled starter batteries and are different internally to cope with the different demands placed on them.

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I have a 17 inch rechargeable tv in the van charge for two hours and approximately 8 hours use . Charge it when running or when enough solar in the day works for me :)
 
autorouter said:
The answer is I don't know. It depends on many things, including how deteriorated your battery is. But it's easy to check - take a measurement just like you did already, then disconnect the battery, wait an hour or two and measure again.

The big problem is that a tiny voltage fluctuation of 1/10 volt is very significant when looking up the state of charge in a table of voltages.
Click to expand...



For the effort involved of doing it one more time I'm intrigued to see how they compare so will do again when I get the opportunity in the next few days. Thanks for this.
 
hymerman said:
As I understand it a lot of the cheaper leisure batteries are just re labelled starter batteries and are different internally to cope with the different demands placed on them.
Click to expand...


After reading the thread "are all batteries born equal" I would agree.
 

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