Deep Cycle AGM Batteries

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Originally Posted by ozscott

I'm happy enough to draw down 50% (but not lower) on my cheapie 130amp. I reckon on still getting 700-1000 cycles. Given it's an electric trolling motor and is used once every few weeks that's a cheap way of getting a great couple of days on the water before a charge. Cheers

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Hi Scott and even with your so called “cheapie” AGM, you can safely discharge that battery down to 20% and expect to get at least 100 to 150 cycles out of the battery.


NOTE, the cycle rate for lead acid batteries is based on how many cycles you can get, down to a specific SoC before the battery capacity is down to 80% of it’s original marked capacity.


So Scott, if you were to use your battery “every few weeks” like you say, then even taking the battery down to 20% SoC EVERY TIME YOU GO FISHING, then you can only expect to get 4 to 6 years use form that battery, and as a “cheapie” 6 years would be a very good life expectancy, even if you never took that battery below 50% SoC.


In other words, even taking your battery no lower than 50% SoC, you would still be lucky to get 6 years out of the battery before it died of natural causes.


Now factor in how much you paid for the battery and how many times you could replace that same battery before the cost got anywhere near the cost of a lithium battery.


You are miles in front just doing what you are doing.

Cheers mate. I'm probably not that hard on my gear in truth but good to know I am on the right track. Those Minn Kota iPilot 2's are really frugal on the juice. I usually do a day then plug in the smart charger to 240v.. Some days I do 2 days in a row then charge. Cheers

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Originally Posted by nick_e

You don't need a BMS for a 12V LiFePO4 battery. They are sealed units of 4 cells with internal cell management.

They are a direct drop in replacement for lead acid, although not usually for starting.

They are definitely expensive though. The capacity is cheaper if you get individual cells, but you need to pay extra for cell management on top.

Edit, it should be noted though that with AGM batteries, you can only use about 30% of the capacity if you want the battery to last its maximum cycle life. You can draw down on a LiFePO4 battery much deeper and it holds a constant voltage for much longer so you cannot compare the Ah ratings apples to apples. You can almost got away with half the capacity you would require for a properly rated AGM system. If you take this into account, the lithium batteries do actually stack up quite well.

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Hi Nick and I have been experimenting and working with lithium batteries for the last 6 years now, and I have developed a few different system for them.

I don't know where you got your "info" from, ( I can guess ), but it is nothing more than the usual advertising B/S used to try to make out lithium batteries are better than they really are!

For a starter, the need to never take a lead acid battery below 60% SoC ONLY applies to people using their lead acid batteries as their main power source, 24/7, and has absolutely nothing to do with how the average RVer uses their batteries.

Furthermore, while some lithium battery suppliers claim their brand of lithium battery can be used as a direct replacement for auxiliary/house batteries, unless you fit a dedicated charging system, specifically designed for lithium batteries, like Tombie is, your lithium batteries will never reach a fully charged state.

While this type of low charging will not harm a lithium battery it does mean your 100Ah lithium battery may only be getting charged to 80% and is a loss the sellers conveniently forget to tell you about.

There are situations where lithium batteries, if set up properly, can offer some big advantages over lead acid batteries, but for the average RVer, they will be nothing more than a grossly over priced diversion from lead acid batteries, and they are highly unlikely to get anywhere near value for money by buying them.

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Originally Posted by drivesafe

Hi Nick and I have been experimenting and working with lithium batteries for the last 6 years now, and I have developed a few different system for them.

I don't know where you got your "info" from, ( I can guess ), but it is nothing more than the usual advertising B/S used to try to make out lithium batteries are better than they really are!

For a starter, the need to never take a lead acid battery below 60% SoC ONLY applies to people using their lead acid batteries as their main power source, 24/7, and has absolutely nothing to do with how the average RVer uses their batteries.

Furthermore, while some lithium battery suppliers claim their brand of lithium battery can be used as a direct replacement for auxiliary/house batteries, unless you fit a dedicated charging system, specifically designed for lithium batteries, like Tombie is, your lithium batteries will never reach a fully charged state.

While this type of low charging will not harm a lithium battery it does mean your 100Ah lithium battery may only be getting charged to 80% and is a loss the sellers conveniently forget to tell you about.

There are situations where lithium batteries, if set up properly, can offer some big advantages over lead acid batteries, but for the average RVer, they will be nothing more than a grossly over priced diversion from lead acid batteries, and they are highly unlikely to get anywhere near value for money by buying them.

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Tim,in what situation for the average 4WDer or RVer do they have a major advantage,apart from weight reduction.

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Originally Posted by scarry

Tim,in what situation for the average 4WDer or RVer do they have a major advantage,apart from weight reduction.

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Space saving - larger usable capacity in smaller form factor
Weight reduction
Longer life span (cycles)
Quicker charge rate

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Originally Posted by scarry

Tim,in what situation for the average 4WDer or RVer do they have a major advantage,apart from weight reduction.

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Hi Paul, as Tombie posted but there specialised situations where a much smaller lithium battery can be used in place of a much larger lead acid battery.

A common use where lithium batteries work better is when there is a continuos high current demand required, such as powering cooking appliances, where the high currents can be catered for by a much smaller bank of lithium batteries as compared with what you would need when using lead acid batteries.

But for the average RVer, where they will be powering a compressor fridge ( or two ), some camp lighting, power for a small inverter used to recharge phone and camera batteries, to power a laptop and/or games consol, while free camping, then you need the exact same amount of battery capacity regardless of whether it is lead acid or lithium batteries.

For example, if you have done a fair bit of free camping and you have established that you regularly use say 100Ah, to meet your needs, then to make sure you do not discharge you battery capacity below 20 SoC you need at least 125Ah of lead acid battery capacity.

As most lithium batteries must not be discharged below 20% SoC then you will need the exact same amount of lithium battery capacity.

This is the sort of use most RVers look at and as such, are highly unlikely to gain anything but a reduced bank account, if they change over to lithiums.

Great information, Tim. Thanks very much!

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Originally Posted by land864

I am looking at having to replace the batteries in both the the Car (auxiliary) and the caravan

Any suggestions on good brands or suppliers please

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I used Full River 120ah for ten years, and were still going strong when my van was hit by lightning which of course destroyed them. I reckon they would have gone for a few more years. The insurance company had Century 120ah batteries fitted. They are now about 5 years old and seem to be doing well. I run 2 x 200w solar panels. 3x 120ah AGM Batteries. 12v Compressor 2 door 185litre fridge. I also use a Zantrex computerised battery conditioner hooked up when the van is in storage. I think this is a big help in the life of my batteries. Expensive Zantrex, about $700 I think, but worth the money.