A Battery for all Occassions

There are many battery chemistry types but lots of different batteries in all shapes and sizes. This is what we have learned. Caution boring stuff ahead.

Over about the last decade we have been studying all the ins and outs of different batteries on countless days and nights and whilst confusing and headache inducing I think we can start to boil down the information so that maybe it helps you understand how different batteries behave and perform. One thing for sure is that battery technology in the last few years has really started picking up momentum with the introduction of affordable chemistry types like Lithium Iron Phosphate (LIFEPO4). As it stands in 2020 as of writing this article there will be two distinct battery chemistry types:

1. Lead Acid Based

2. Lithium Based

If searching for batteries we can break it down into the most common forms:

1. Lead Acid - Absorbed Glass Mat (AGM)

2. Lead Acid - Gel

3. Lead Acid - Flooded 

4. Lithium Iron Phosphate

These are also referred to as VRLA batteries or Valve Regulated Lead Acid as they are fully sealed maintenance free. In the event of battery overcharging or internal failure they have valves to release any build up up of gas pressure. The other sort is the traditional flooded lead acid battery you might see in a car. If you want to use this style of battery in a storage system be prepared to really understand how to look after them as electrolyte levels must be carefully monitored and maintained.

There are other battery types you might come across that are less common but nevertheless very good:

1. Lead Acid - Carbon or Lead Carbon

2. Lead Acid - Crystal

3. Lithium Titanate

3. Zinc Bromide Flow (these are seriously cool look them up).

For the most part though the batteries you would be most likely to end up purchasing for storage systems will be Gel, AGM or LIFEPO4. At Mannerfarm we use all three of these common types so based on experience and research we can say a few things about them, but first some boring facts about batteries that need to be considered before investing your hard earned dollars.

Manufacturers Specifications

Over the glossy brochures and slick looking packaging we cannot stress how important it is to understand the batteries specifications because they range quite a bit from manufacturer to manufacturer and of course only buy from reputable manufacturers. So here are the things you need to consider from most important to just less than most important.

#1 Cycle Life Vs Depth of Discharge

This is the big one and determines how long you will expect to get out of your battery system. No matter the chemistry type all batteries degrade with age and more importantly with use. The charge and discharge of a battery is termed a cycle. A cycle isn't defined as going from 100% to 0% (well it could be if you do it - but don't) but rather going from a state of charged to a state of discharged to a certain level then charged again. How far you discharge your battery for that cycle is a key part of your batteries cycle life. Never buy a battery for your storage system if the manufacturer does not clearly supply a cycle life. Most Lead Acid batteries will display a cycle life at 30% discharge eg: 1500 Cycles. The deeper you discharge a battery the less cycles you will expect to get from it.

This is where a good quality LIFEPO4 battery kicks the stuffing out of Lead Acid batteries. This chemistry type typically rates its cycle life based on an 80% discharge and the number of cycles is generally way higher. This means you can get more energy out of a LIFEPO4 battery type with more cycles. Typically you might see 1500 Cycles @ 30% for Lead Acid and 4000 Cycles at 80% for LIFEPO4.

#2 Usable Capacity

Just because your shiny new battery trumpets it has 300ah doesn't mean that is what you are going to get out of it. When sizing a battery system chemistry type really matters. It is a common and well understood industry fact that for lead acid based batteries you budget for a usable capacity of around 50%. So for that 300ah battery expect to use at most 150ah. Sure you can use more but discharging a lead acid below 50% is really going to reduce its cycle life (like a lot). AGM and Gel batteries are known as deep cycle batteries. It means you can discharge them to a very low level and they will recover. This doesn't mean its a good idea to do it. It just means if you have to or accidentally do so its not going to destroy the battery.

Battery capacity changes depending on temperature. The colder it is the less capacity you have and the hotter it gets the more capacity you get. This is why batteries tend to drop dead in winter. Internal resistance increases with cold and decreases with heat. This doesn't mean you should have a hot battery. Hot batteries die just as quickly as cold batteries. Capacity of a battery is therefore calculated typically at a room temperature of 25 degrees celcius. Any variance in this temperature alters the expected capacity generally rated in millivolts per degree. This is why many battery charge controllers have temperature probes.

So finally here comes the last kick in the capacity game, "Peukert's Law". Yep the harder you push a battery when drawing from it the less you get from it. Why? Well it has to do with internal resistance and that resistance sucking energy out of the battery as heat. That's about as simple as I can put it. This is why the battery C-Rating is important and typically your see the C-Rating measured at 20 hours. This means if you draw "X" amps over a 20 hour period you get "Y" capacity at 25 degrees celcius.

This is where LIFEPO4 chemistry type gives Lead Acid a whack to the face. LIFEPO4 has really low internal resistance which means that not only can you draw much higher loads from it without suffering from our old mate "Peukert" it charges way better. When charging the same sort of effect is present just in reverse. The harder you push (charge) the harder it pushes back (from internal resistance and this produces heat). This is less of an issue for Lead Acid at low discharge but increases as the charge level goes up (hence the different charge cycles - Bulk, Absorb and Float).

#3 Age

You know how good freshly baked bread smells Vs stale bread? Well whilst batteries don't smell like that they definitely suffer like bread from age. Its important to find out before buying a battery when they where manufactured. This is because all batteries once that chemical reaction starts on first charge from the manufacturer are on the slow decline to death. All batteries have a shelf life which can be termed their chemical life. whether you use the battery or not the clock is ticking on it. For AGM, Gel and LIFEPO4 batteries this is generally in the order of 10-20 years. Where LIFEPO4 gives Lead Acid a boot up the backside is it does not need a freshening charge anywhere near as often as Lead Acid so tend to last way better. Typically Lead Acid batteries need a freshening charge every 6 months or so as opposed to LIFEPO4 which can be years.

As you cycle your battery its capacity will diminish. How much it diminishes can only really be calculated using a test whereby you charge the battery to 100% then discharge it at its designated C-rating and taking into consideration temperature whilst measuring consumption using a good battery monitor until the battery is depleted. For Lead Acid batteries we don't really recommend doing this as it can further degrade or kill the battery. All battery systems should have a good battery monitor so you are going to know via observation how your system is performing anyway.

The Mannerfarm Verdict

You might be thinking that it seems LIFEPO4 is the obvious choice. Well its not that simple because there are some other things you need to consider. Lead Acid batteries have been around a LONG time and they are a well established, reliable, safe and predictable battery. So much of the knowledge and expertise in batteries revolve around this chemistry type. You have to seriously abuse a Gel or AGM battery to kill it, take it from us we have tried (inadvertently). You can build some seriously large battery banks with Lead Acid batteries really easily. Its just a matter of doing your maths and sizing it correctly to get the best performance Vs dollars out of it without over capitalising (spending too much coin). 

A typical reason used in the past to not use LIFEPO4 batteries has been cost. The important thing to consider is cost Vs usable capacity and cycle life. A real world example of this is a comparison between our 300ah AGM and our 100ah Lithium. Each battery cost about the same being $630 for the AGM and $799 for the LIFEPO4. So let's look at usable capacity and cycle life of each:

AGM 300ah: 1600 Cycles @ 30% = 90ah

LIFEPO4: 4000 Cycles @ 80% = 80ah

Based on usable capacity at that cycle life its clear LIFEPO4 battery gives best bang for buck.

The other thing worth noting though is LIFEPO4 batteries utilise additional internal electronics in what is called a battery management system or BMS. They look like a regular 12V battery from the outside but actually if you open one they have a BMS that connects to each individual lithium cell (each cell is its own battery). The BMS is responsible for making sure each cell in the pack is balanced voltage wise. It should also perform functions such as over discharge disconnect, over charge disconnect, low and high temperature disconnect. If the BMS fails the battery pack fails.

So finally after all this waffle here is our view on selecting a battery system and again this is just our view based on experience, feel free to come to your own conclusion after all its your money:

1. Caravan/Tiny Home/Shack: I would definitely go LIFEPO4 for this type of application. Lead Acids are heavy (did I mention that), like really heavy compared to LIFEPO4. Also space will be premium so you get more capacity for less weight and physical size out of LIFEPO4. Also you need less charging capacity because LIFEPO4 absorbs energy more readily and this is something we have really noticed.

2. Off Grid Large Home: I would still be looking at lead acid for larger battery systems and in such a case I would be choosing 2V Gel batteries that you connect in series to get your 12V. You can make some seriously big systems using these batteries and they are happy in any configuration 12V, 24V, 36V, 48V etc... Because its a home space presumably would not be an issue or the weight.

3. Hybrid: Depends on size but I would lean towards LIFEPO4.

So what about AGM batteries... hmmm sorry old boy I love you and all but its time to think about retirement. You have served us well but like all things including us there is an expiry date.