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Deep cycle batteries (again)


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On behalf (but might also be for myself soon too).

What’s best value 6V AGM options currently around (to create 2x2 12V house bank)?


1. 250Ah or more each

2. Max dimensions: L280 x W180 x H300

3. Fair quality & price ie mid-point

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is that dimension per battery or the battery box size?

A 225 - 250ah (T105 form) is 260 L x 181 W x 270-290H (Lifeline has a 300ah 6V with this footprint, 328 H)

A 300 - 325ah (L16 form) is 310L x 183W x 370h

As for AGM brands, Lifeline are the best and you pay for them. I have AGM's from Enertec and so far so good, altho I preferred the Toyama hybrid gels they used to sell.


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I'm now running "The NZ Electric Boat Co" up in Kerikeri so I have acquired a bit of knowledge on this subject, we've been equipping a few boats with propulsion batteries.

For our own hire boats which are intensively used commercially, if they can take the weight then we use conventional flooded Trojan L16H ("Motive" branded) lead acid batteries. These are about the heaviest duty 6v traction batteries out there and high quality. You can discharge them quite deeply while still getting a decent cycle life.

If you buy a lead acid battery which has really good deep cycling performance then you might need less nominal amp hours capacity because twice as much of that capacity is actually usable without damaging the battery. 

One of our boats came with Sonnenschien 6v gel batteries, maintenance free. If you observe the slightly lower charge voltage then these are very long lived too and no need to top them up. Sonnenschien are available in NZ.

We've heard some good things about the Narada lead carbon batteries, some people have put a lot of deep cycles on them in a short time and they are still going strong, but they've not been around for a lot of years so not 100% proven. Certainly worth a look though.

A good guide as to which is the best lead acid brand is simply to compare the weight at the same capacity. The heaviest brand will probably last the longest. Make sure you compare like with like... the C10 capacity of one battery is not comparable to the C20 capacity of another and some sellers quote capacity at different discharge rates. C10 is the capacity if the discharge is over 10 hours, C20 measured over 20 hours. Some quote C100 which is very optimistic!

For our catamarans, which are more weight sensitive, we use lithium. enertec provide fantastic local support and their Juice Pro batteries are worth the money, but it is a lot of money. Having had one apart I can tell you these are not just assembled from Chinese components, all the circuit boards are custom made for enertec and the batteries, including all the BMS boards, are genuinely designed in NZ. They even customised the software for us. We have built some custom waterproof versions of the enertec battery using their boards.

The Torqeedo lithium batteries are very good too if you have a 24v system and they are inherently waterproof.

The enertec batteries are LiFePo4 chemistry which is inherently safe. The Torqeedo batteries use a more exotic chemistry which is about 30% lighter and have lots of safety features to mitigate that. There's never been any safety issue.

We can supply either of the above lithium brands at a good price (yeah that's a plug! mention crew.org and I'll donate to the site if you buy something)

> Why not 2 x large 12v AGMs?  Much less hassle than flooded. 

The key with lead acid is to use the biggest, heaviest duty cells you can, that way they will last much longer (eg one string of 400ah cells is better than two strings of 200ah cells in parallel). 12v batteries contain 6 relatively small cells. If you try to put big heavy duty cells in a 12v battery then the battery will become huge and impossible to lift. therefore it's better to split it half and use two 6v batteries, or even 6 2v batteries for a really big battery bank. So generally the best option is one string of huge cells all in series.

The possible exception is if you are going offshore and want some redundancy in the system, if you have two strings of cells in parallel then if a cell fails in one string you can disconnect it and still use the other string.

So, you asked about AGM...

We have Victron Supercycle AGM house batteries on our live-aboard catamaran, very happy indeed with them. Bought them when we were in Europe, can't find a source for them in NZ at the moment though. 4x200ah 12v in parallel because that's what was available. If they had been available then a better option would have been 4x6v 400ah in series and parallel.

Prior to that we had a bank of Haze / Eaton AGM 12v cells, second hand from a vodafone cellphone tower backup bank. Despite their age and small cells they lasted well (9x 12v 100ah batteries in parallel). Again, chosen due to availability more than anything. If you can find used batteries from a quality brand which have been in a well maintained UPS install not doing many cycles, not being overcharged, then they will probably outlast brand new batteries from a cheaper brand. Make sure you really know their history though.

Many people are still going lead acid on the basis that lithium will be much cheaper so they'll switch to lithium (or some new) technology when those lead acid batteries reach end of life. Others want something which will last a lifetime and at a fraction of the weight the Juice Pro is built to do that.

Hope that info helps rather than confuses!



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