AGM vs lithium batteries; what’s better, and why?
Some time ago, we made the swap in our Hybrid Camper and Isuzu Dmax from AGM (or Lead Acid) batteries to lithium batteries, and there were a huge number of reasons that contributed to doing so. However, today I want to cover the basics, and look at every single difference between lead acid (and AGM) batteries, and lithium batteries.
Please note that this post refers only to 12V batteries, and we are talking about LiPo4 as lithium.
Like everything, lithium batteries started off hugely expensive, and with time have become very cost effective. In fact, today you can purchase 12V lithium batteries for a similar price to a high end AGM or lead acid battery, and that makes choosing easier.
Weight
The first thing that everyone finds out when comparing lead acid batteries to lithium’s is the difference in weight, and it really is quite staggering. A 100aH lead acid battery will weigh in at around 25kg.
A 100ah lithium battery weighs in at around 12kg, or basically half of the weight. However, its far better than just that; the usable capacity of both is vastly different, which also swings in the lithium batteries favour, but we cover that more below.
However, for a practical example, I removed 240aH of lead acid batteries that were 30kg each from our hybrid camper, and replaced it with 340aH of lithium batteries that were only 44kg.
Usable capacity (depth of discharge)
If you have AGM batteries, and run them until no appliance wants to work anymore, you can do damage to them. The general consensus has long been using 50% of the capacity is about the maximum you want to go to, without doing damage to the battery itself. This is a guide only, and not exact science, in order to preserve the batteries longevity, and you can go lower, but you need to recharge them and not leave them at a low state.
Using this guide, it means for a 100ah lead acid battery, you get about 50ah of usable capacity. In the grand scheme of things the lifespan generally is what falls over first, and you can probably go to 60 or 80% depth of discharge (using 60 – 80% of the 100aH), but its still less than lithium batteries (and most people specify it from a 50% DOD)
Lithium batteries can be discharged from 100%, right down to 0%. Ideally, you use a bit less than this, but they are quite happy being full, and completely empty, which gives you a massive increase in usable capacity.
If you swap a 100aH AGM battery with a 100aH lithium, most people suggest you are getting around 50% extra usable capacity, in conjunction with the 50% less weight. You can literally take a 200aH lead acid battery, that weighs about 50kg, and swap it out for a single 100aH lithium battery that weighs 12kg, and you’ll essentially get the same usable capacity.
Now, this isn’t exactly true, as if you are only using 50% of your AGM capacity and you then start using 100% of a lithium, you have no buffer and you will run out of energy if you use a little bit more. My advice then, is to fit slightly more than double the lithium capacity of your AGM batteries.
Number of cycles
Most lead acid batteries are good for about 1500 cycles, but not using the full 100%. The more you consume, the less cycles you get (but essentially the same energy amount can be drawn). Lithium batteries tend to start off at about 2000 cycles from 100 – 0%, and they go up from there, all the way to 3500 or even 4000 cycles.
That is an obscene number of cycles, and presuming the batteries don’t die of old age, increases your use substantially. Please know this is a theoretical number, and there are a lot of lithium batteries that do not reach the quoted life cycles before something goes wrong, and that’s where a solid lithium battery warranty is very valuable.
Maximum discharge rate
You’ve probably heard, or seen a number of people installing microwaves, coffee machines, air fryers and induction cooktops in their 4WD, camper or Caravan, and it can be done with lithium batteries, but is almost impossible to do with lead acid batteries.
The reason is simple; lead acid batteries are not designed for huge discharge rates, and when you pull a lot of power from them in a short period, the batteries will get damaged and will fail earlier. Lithium battery discharge rates vary a lot, but some of the high end batteries will do a continuous discharge of 250 amps, which is around 3000W, and is a lot of power!
An AGM might be good for 40 or 50 amps at best, but you are really pushing the friendship, and that means if you want to run power hungry devices without a generator, lithium batteries are really the only option. Yes, it can be done with AGM batteries if you have enough of them, and the specs match, but they are far less suitable for doing so than lithium batteries.
Our 340aH of Renogy Lithium Batteries can discharge at 3000W, which is around 250 amps, and its absolutely cranking power out.
Maximum charge rate
On the flip side of the coin, lithium batteries can be charged at a much faster rate as well. Its not uncommon to have a 100amp maximum charge rate on a lithium battery, but doing this to a lead acid battery would fry it in no time.
Every battery you purchase should come with a list of specifications, and you need to adhere to them. It is worth noting that its quite hard to put 100 amps into a battery; there’s no DCDC chargers on the market that would do this, and even if they could, many alternators wouldn’t handle the current either.
Charging 100 amps from mains power is also not very easy, but it is possible, and the same with solar.
Our 600W of Renogy Solar Panels on our hybrid top out at about 45 – 50 amps, and that’s not even a big system. If we run the extra 120W panel on the roof, plus a 200W blanket, sometimes we’ll see 65 amps going into the battery, and doing this to two AGM batteries would cook them.
Some caravans have 1600 – 2000W of solar on their roof, and can easily pump in 100 amps an hour on a cool sunny day, and you simply can’t do this with AGM batteries.
Lifespan
Lead acid batteries never seem to last very long. 3 years is probably fairly average, with some of the better brands making it to 5 or 7 years, but getting any longer than this is rare. That means every 3 – 7 years you are up for new batteries.
Lithium batteries on the other hand can be good for up to 20 years, which is helpful as the number of cycles that they can do makes them need it.
Our Renogy Lithium Batteries in the hybrid are rated for 2000 cycles, which is on the lower end of the scale. However, if we discharged and charged them completely every single day, we’d still get 5 and a half years from them.
We plan on being on the road for 1 – 2 years, and we’re not discharging them the full cycle amount, which means they should last a lot longer. It really is obscene how long they’ll last for, but it will be interesting to see which lithium battery brands actually live a solid life, and which ones fail early.
Cost to purchase
There’s no denying that lithium batteries, apple for apple are more expensive, and often far more expensive. A decent 100aH lead acid battery will sting you about $350. Most 100aH lithium batteries start off at around $600, and then work their way up to $2000 a battery.
Lithium batteries are far more expensive, but, you need to think about the actual cost over its lifespan (if you intend on keeping it long term) as the results can be quite surprising.
Cost per amp hour
If you are actually considering the total cost, you need to look at cost per watt or amp hour, and we’ll do a practical example. Lets say you have a 100 amp hour lead acid battery, which is depleted to 50% every day, and is good for 1500 cycles. That’s 50 amp hours multiplied by 1500, giving you 75,000 amp hours.
A lithium battery on the other hand, that is good for 2500 cycles at 100%, will give you 250,000 amp hours. If you pay $350 for a lead acid battery, that’s 0.46 cents per amp hour. With the lithium battery, you are looking at $800, and you’d get 0.32 cents per amp hour. Even if you paid $1200, its still on par with the 0.46 cents per amp hour, and you can get them for a lot less than this.
Charging requirements
Lithium batteries are supposed to be charged with a charger that has a lithium battery profile. That means a different charging curve, without the equalisation phase. Some lithium battery manufacturers refer to their batteries as ‘drop in lead acid replacements’, which is stretching the truth and really quite dishonest marketing. If you see this, tread cautiously.
Yes, you can use a normal lead acid battery to charge a lithium, but it won’t work as well as it should, and will take a lot longer to charge.
If you want to move to lithium, make sure your existing DCDC, or solar regulator has a lithium charge profile.
DIY lithium batteries
With so much information online, its entirely possible to build your own lithium battery. We did exactly that in our Isuzu Dmax, and have 230aH of prismatic cells hooked to a 150 amp Daly BMS, and its been running our fridge, lights, 2000W Renogy Inverter and doing a heap of work full time for some time now.
This can be quite an economical way to get a good quality, cheap battery, but there’s also some really cheap fully assembled lithium batteries on the market today that make building you own one seem a bit pointless.
Lithium battery brands
There are more lithium batteries on the market now than you can poke a stick at, and we’ve covered a heap of them already in our lithium battery buyers guide.
You might not need the most expensive one on the market, but read the specifications, and get something that is going to suit your needs.
Should you move to 12V lithium batteries?
Ultimately, that depends on your individual circumstances. We did it for a whole heap of reasons, and absolutely love the swap. It wasn’t cheap though, and if it weren’t for the fact that our batteries were in need of replacement soon, and that we were going full time on a lap of Australia we would have held off.
Like household solar systems, I can only see the price of 12V lithium batteries continuing to come down, and it wont be long before buying a lead acid battery just doesn’t make any sense at all.
What do you need? Are lithium batteries going to help you achieve this?
Do you run lithium batteries? What do you think of them?
