Lithium vs AGM BatteriesThis would be the most often asked question on camping groups and pages and the answers given by commenters range from sensible to downright uninformed and silly.

So I feel it’s a good time to provide intelligent information – especially as Spring is approaching and many are getting ready to install or upgrade their batteries.

Lead acid batteries have been around since last century and while much improvedLithium Ion and Lithium Iron Phosphate types provide much higher energy density and other improvements than lead acid types. They are becoming more commonly installed now that prices have come down to reasonable levels. While many still complain about the price, the reality is that the lithium used in this type will always cost more than the ingredients in lead acid AGM batteries so we can’t expect the cost of quality lithium batteries to come down to that of a quality AGM anytime soon. Sure, there are cheaper lithium batteries on the market but there are serious drawbacks to them and I’ll talk about them in more detail later. However, when you factor in the expected lifespan and the usable capacity of lithium batteries, you might be surprised how close they come in value for money to AGM batteries.

Another myth often quoted is that lithium batteries are prone to explode. Batteries used in the ‘RV’ market are not the same as those used currently in electric vehicles. EVs usually use Lithium Ion cells, much the same as used in laptop batteries, but have sophisticated electronic systems to protect their battery packs. RV batteries use Lithium Iron Phosphate (LiFePo4) cells – which are inherently far safer and are very unlikely to overheat or explode in normal use and the BMS or battery management systems in them ensures they are never over charged or discharged.

A big advantage of Lithium Iron Phosphate (let’s call them LiFePo4 from now on to save space) batteries is their ability to be safely discharged to down to near empty and then recharged far more quickly than AGM batteries. Regardless of what you might read, lead acid batteries cannot be discharged much further than 50% of their capacity if you want to ensure they have a reasonable lifespan. Also, LiFePo4 batteries can deliver higher current, which is good if an inverter is needed to run 240V appliances like induction cooktops which are becoming more popular now for example. As I also mentioned, this kind of battery can be charged at higher currents and hence much quicker than AGMs, either from a good-sized solar set up or from the vehicle’s alternator. This means we can use our batteries almost to zero overnight and not have to worry so much about if they will receive a good charge quickly the next day.

To elaborate more on the points above, the Ah rating of lead acid AGMs are usually measured at 0.05C (this means 5% of the Ah rating) – so for example a 100Ah rated battery should deliver 5 amps for 20 hours before it is totally flat. Of course, discharging an AGM that far severely limits it’s lifespan so taking it down to 50% is the recommended level, so that means it can actually deliver 5 amps for only 10 hours. By comparison, a quality 100Ah LiFePo4 battery can safely deliver 0.5C or 50 amps or more for extended periods of time before it is discharged down to 20% of its capacity (a safe level to get the maximum lifespan). This is why you need much higher capacity AGMs to be able to run for example an inverter while a single quality 100Ah LiFePo4 can handle one easily.

Weight is another important factor, if you have ever lifted a large AGM into a caravan boot, you will know what I mean – a quality AGM of 130Ah+ capacity weighs about 35Kgs. By comparison, the same Ah rating LiFePo4 battery is around 12Kg. For installations that require 200Ah or more, this can be a serious issue depending on where they are installed. Adding 70Kg to a caravan front boot can seriously affect the tow ball weight for example.

For a ‘real world’ example, we have a 130Ah AGM battery in our caravan to run the lights (LED), TV, water pump and also power our 60l portable fridge in freezer mode. We need cloudless days for the solar to be able to recharge the battery fully, two days of patchy cloud cover means we have to either plug in to 240V or run the car for an hour or so which we don’t like to do. In comparison, a 100Ah LiFePo4 battery would be able to easily handle that situation and we could save more than 20kgs of weight in the process!

Do be aware though, of cheap LiFePo4 batteries. Like anything, price is a good indication of quality and this definitely applies to RV batteries (especially lithium types) and there are many tests to be seen online, if you search hard enough, of some of the cheaper brands on the market in Australia. The usual result is that the actual Ah rating is much less than what they are sold as. It might not be important if your battery needs are minimal but paying over $500 for a 100Ah branded LiFePo4 that is really 50-60Ah compared to around $300 for the same effective capacity 100Ah lead acid AGM just makes no sense to me. Be aware of the positive, glowing ‘reviews’ too – I suspect that many are either posted by the importer of the batteries (they commonly use cheap cells and BMS systems) or are from users that run a few lights and a TV not a 12V compressor fridge.

I discuss this in much more detail (including what to watch out for when buying LiFePo4 batteries) in the latest version of the electrical guide which is now out and can be downloaded from this blog. I hope this has cleared up the situation somewhat for you.

Andy