Battery advice - is it BS?

[philmarks]

I'm looking to renew my domestic batteries, currently 2 x 220 ah lead acid.

I've been offered Optima Blue AGM, 75ah. They are an optima dealer and the proprietor says that because of their high CCA, one is equivalent to 1 x 200 ah lead acid. Now, I know that lead acid only has 50% or so of its nominal capacity available for use and I assume that AGM should not be fully discharged, but even so, this seems supposed near-equivalence sounds like bullshit to me.

Any advice welcome from forumites.

Thanks

 

[Bru]

AFAIC it's bull

AGM batteries have a number of advantages but they still give their best whole life performance if discharged to no more than 50% capacity just like any other lead acid battery (which they still are) and a 75ah battery is a 75ah battery not a 200ah battery.

Even if you fully discharged the AGM battery it is only going to deliver 75ah and a 200ah battery discharged to 50% will deliver 100ah! (OK, for the technical nerds that is more than somewhat simplistic but it suffices for this discussion)

CCA (Cold Cranking Amps) is of little relevance to a domestic battery installation and all that being able to deliver a higher current will achieve is a faster discharge of the battery anyway

 

[pvb]

Yes, you're being told porkies.

 

[VicS]

CCA is only relevant for engine starting ... it stands for cold cranking amps. It gives an indication of how many amps can be delivered for engine starting. ( MCA is similar but measured at a different temperature)

Ah isthe relevant figure for a domestic battery. Its a measure of how much juice is stored, 75 Ah is only 75 Ah. 200 Ah is over 2.5 times as much

 

[lpdsn]

I'm looking to renew my domestic batteries, currently 2 x 220 ah lead acid.

I've been offered Optima Blue AGM, 75ah. They are an optima dealer and the proprietor says that because of their high CCA, one is equivalent to 1 x 200 ah lead acid. Now, I know that lead acid only has 50% or so of its nominal capacity available for use and I assume that AGM should not be fully discharged, but even so, this seems supposed near-equivalence sounds like bullshit to me.

Any advice welcome from forumites.

Thanks

Not bullshit necessarily, just a misunderstanding of your requirements. Sounds like they've assumed the main purpose of your 2 X 220Ah batteries is engine starting.

 

[Bru]

Not bullshit necessarily, just a misunderstanding of your requirements. Sounds like they've assumed the main purpose of your 2 X 220Ah batteries is engine starting.

Not really, they are claiming that a 75ah AGM battery is the equivalent of a 200ah flooded cell battery. That's BS!

Edit:

In a purely starting application the higher CCA might be relevant ... I'#ll go look at some figures ...

 

[lpdsn]

Not really, they are claiming that a 75ah AGM battery is the equivalent of a 200ah flooded cell battery. That's BS!

Edit:

In a purely starting application the higher CCA might be relevant ... I'#ll go look at some figures ...

Was just about to reply. As you've spotted my point is that they may have been focusing on the CCA rather than deep cycle capacity. Their advice isn't good, but I wouldn't call it BS unless I thought there was an intention to mislead.

 

[Bru]

Was just about to reply. As you've spotted my point is that they may have been focusing on the CCA rather than deep cycle capacity. Their advice isn't good, but I wouldn't call it BS unless I thought there was an intention to mislead.

If that's the case they're kind've right in a way in that those Optima batteries have a heck of a CCA capability for their size. It also seems that they can be hammered hard on recharge. True deep cycle batteries tend to be light on CCA capability which distorts it even further but I can't actually find a battery to line up as an equivalent to the Optima even taking CCA as the primary criteria (on that criteria alone a 75ah Optima would be the equivalent of about 5 Trojan 200ah flooded cell batteries!!!!!)

ANyway, bulldust or mistake, the advice given to the OP is bad!

 

[lpdsn]

ANyway, bulldust or mistake, the advice given to the OP is bad!

Agreed.

 

[Mistroma]

I can't imagine that anyone in the business of selling batteries would immediately assume 4400Ah batteries on a boat were primarily for engine starting and jump straight to comparison of CCA figures. They should realise that they are more likely to be for domestic use.

Doesn't stop someone deliberately picking on CCA in order to make a sale.

 

[lpdsn]

Doesn't stop someone deliberately picking on CCA in order to make a sale.

Would he make a lot more profit out of one 75Ah battery than out of two 220Ah batteries?

Jeez, I'm beginning to sound like a defence lawyer for this bloke, but it just doesn't sound like a deliberate mistake to me.

 

[Danny]

Would he make a lot more profit out of one 75Ah battery than out of two 220Ah batteries?

Jeez, I'm beginning to sound like a defence lawyer for this bloke, but it just doesn't sound like a deliberate mistake to me.

I think the original post said the claim was that the Optima was equivalent to one 200Ah flooded - not two. And it probably is - in price!

 

[PCUK]

Optima Blue Top are fantastic batteries. I have one about 16 years old (this has been totally flat on several occasions for months but still charges just fine and holds the charge for about 18 months if not used) as well as several nearly new ones. We use the old one to start a GM V8 6.5 diesel and it never has any trouble doing it.

 

[philmarks]

Thank you all. I had told him that they were required for domestic purposes. I had asked for deep cycle and he offered the Optimas as they were dual purpose. I could of course go for multiple optimas to give the ah equivalent - I have the space, and would save some weight. However the cost is prohibitive.

 

[lpdsn]

Thank you all. I had told him that they were required for domestic purposes. I had asked for deep cycle and he offered the Optimas as they were dual purpose. I could of course go for multiple optimas to give the ah equivalent - I have the space, and would save some weight. However the cost is prohibitive.

You'd be paying all that extra money for the CCA's which you don't need. Better to get batteries that meet your requirements for domestic batteries at a lower price. Get real deep cycle heavy duty batteries if you want to splash out a bit (rather than the leisure deep cycle the rest of us can afford).