In this post I want to motivate you to think ahead over 5 - 10 years into the future - and also to not be mislead by marketing and battery ratings.
I first want to explain
- why having batteries is better
- why if you have a choice, Lithium-Ion batteries are more economical for your network.
Batteries vs no batteries
If you are faced with a choice of how to spend your money - whether you should install more network points, or fewer network points, but each point having a battery, which should you choose?
You should always opt for having batteries. Why? Network reliability. The only way to build a network that will grow, is to make sure it is reliable. It is for the same reason you should not build a house on the sand.
The bedrock of a network is reliability. The reason is that if you have a network point that depends on another on and that depends on another one, if the first one is unreliable, then all the others are unreliable - but not only that, if the second one is also unreliable then the third one will be even more unreliable. A network that is unreliable, even if it is the only network available, will make it difficult to use. If someone has to travel to use it, and then they can’t use it, they will be less likely to travel to it to use it in the future. Things are used best if you can make plans around it. If it is unreliable you can’t make any plans and that also limits what you can do. If you arranged for someone to meet you online, or to help you with something, and for some reason now that can’t happen, then you have wasted time for everyone involved as you have to reschedule. What if this was a relationship or meeting that could have helped you a lot - and what if due to unreliability this opportunity will be lost forever? Often that is not the case, but sometimes it is. The long and the short of it is that an unreliable network will not just grow a bit slower than a reliable one, but a lot.
The thing that affects network reliability the most, is electricity.
Installing batteries is the best investment you can make on a network. Flowing from this, installing battery protection is the second best investment you can make. This is the most expensive part, so getting this right will set you up for success. Everything else will be cheap to upgrade or replace by comparison.
There might be better solutions in 5 - 10 years from now, but today, in 2022, Lithium Ion batteries will always cost less to run, if you consider the lifetime of the system.
Why?
First you have to understand the battery ratings. A 100Ah Lithium Ion Battery of the same voltage, is about 5 times better than a lead acid battery.
Why?
Consider the rating. 100Ah. What does it mean?
There are many resources available on the internet that you can study. I will give you the summary (the “TLDR” - “too long, didn’t read”). Here it is.
To be able to compare batteries, you have to calculate the “Watt-Hour” rating. That is how many Watts it can power, for how many hours.
For batteries it is simple. Multiply the A by the V. VA and W is the same thing for a battery. Again you can read a lot about this by just searching for “Power Factor”, but for circuit where everything is DC, it is the same, and you can compare it directly.
So say you have a 100Ah 12V battery. A 12V battery is actually a 12.7V battery. So 100Ah x 12.7V = 1270VAh = 1270Wh.
Simplified, you should be able to run a 1270W device for 1 hour. Or a 127W device for 10 hours. The real problem is that this is not true.
Why?
Because the 100Ah rating is used for marketing. It depends on the minimum voltage that you can run the battery to, and is usually based on a minimum voltage of 10.5V. The real problem is that at 10.5V the battery will not even last half a year if you use it every day. The battery manufacturer does not care, because it means that if you use the battery every day, after just a few months you will have to buy a new one.
Why?
This depends on the battery chemistry. If you are interested in battery chemistry, you can do searches. The least practical, but most interesting will be if you search “Electronegativity” A more useful search will be “battery chemistry”. An even more practical search will be “battery care”. Eg. Battery Basics - Guide to Batteries | BatteryStuff
So how can you compare batteries correctly?
To compare the 100AH 12.7V battery correctly to it’s Lithium-Ion battery equivalent, you have to measure its Ah rating based on a cut-off voltage that will make it last at least 30-50% as long as a Lithium battery. That means calculating how many Wh it has when it drops to just 11.7V. You can consult the battery specifications to see what a good cut off voltage is. Usually the difference between making lead acid battery last double as long is as little as 11.4V vs 11.7V. That means at 11.7V you might have 20Ah, and at 11.4V you might have 40Ah, but at 11.7V the battery might last 5 years where if you drain it to 11.4V it might only last 2.5 years.* So this makes a big difference. If you drain it to 10.5V it might be 100Ah, but it will only last a few months.
Okay, but how do we compare it easily?
Divide the rating of the lead acid battery by 5. So for the 100Ah 12.7V battery, you only use 20Ah. 20 x 12.7 = 254Wh. If you treat the battery like a 254Wh battery, it will last a few years. You can divide it by 4 to get 25Ah x 12.7V = 317Wh. Or by 3 to get 33Ah x 12.7V = 419Wh. But it won’t last nearly as long in years, even at best, a Lithium based battery will last more than double as long.
This means that you must not compare a 100Ah x 12.7V = 1270Wh Lead Acid battery to a 1270Wh Lithium battery. It will make the Lithium based battery look 5x - 10x more expensive. But it is a false comparison.
Okay so how do you compare it directly?
Multiply it by a fair rating. 100Ah divided by 5. so for a 100Ah battery, it’s 20Ah x 12.7 = 254Wh. So you should compare it to a 254Wh Lithium based battery. Even so, it should cost about half as much to be price competitive.
How so?
Because of the cycle count. Even the best Lead Acid batteries, can only last 1500 cycles, if you never drop the voltage below 11.7V. The worst quality Lithium Ion batteries can manage that. More often Lead Acid batteries degrade long before that so that you are lucky to get 500 full cycles from it. You do get poor quality Lihium based batteries too… so.
Always insist on a warranty, no matter what the specification says.
Manufacturers are reluctant to warrant Lead Acid batteries, because of how easy it is to damage them. Lithium Ion battery packs always come with protection circuitry (aka. a BMS or Battery Management System) built in, so it is easy for a manufacturer to warrant a Lithium Ion battery. If they are not willing to do so, then do not buy it. You can buy unprotected cells - and you can damage them with just a single charge, if you do not use a BMS or if you do not limit the current or the voltage. This is a matter for another post.
An example
Suppose a 12V “100Ah” lead acid battery costs $150. Usually a similarly rated 12V 100Ah Lithium Ion battery will cost closer to $400. But this is the wrong comparison.
You must compare the 12V 100Ah Lead Acid battery with a 12V 20Ah Lithium Ion battery. The former might cost $150, and the latter might cost $150 - $300 depending on the quality. Even at $300 you will be saving money - if the warranty holds - because the Lithium Ion battery should last 1500 - 3000 cycles, whereas the Lead Acid battery will only last 500 - 1500 cycles. So over a period of time you have to factor in the price of 2 or more Lead Acid batteries vs. one Lithium based battery.
To summarize
- To compare Lead Acid to Lithium, divide the Lead Acid Ah / 5. Multiply V by Ah to get Wh for a fair comparison across technologies.
- Always add more batteries than you think are necessary. Adding more batteries will make all the batteries last longer.
- Always install a charge controller or low voltage cut off switch - AND CALIBRATE IT correctly, if you use a Lead Acid battery. Consult the spec sheet or manuals for the specifics.
- Always test before you buy in bulk - or buy what someone you trust, has tested.
Unless you have absolutely no other option, or you can manufacture your own batteries at less than half the market rate, always obtain the best Lithium based batteries that you can.
Some people will argue that Lead Acid batteries are not that bad. If you believe that, test it for yourself, and use a lower divisor to compare, for example divide the Lead Acid battery rating by 2 instead of 5. If this turns out to be the case, then you have almost certainly only been able to obtain used Lithium Ion cells, or damaged ones.
If you can gain access to old laptop battery packs - their BMS counts the number of cycles they’ve been used, and some disable the pack when it gets to 500. If you replace the BMS - or reset it - you can often get another 1000 cycles - 2x to 3x the life - from the same cells, so a lot of people make a living recycling these. Even so, the amount of time and effort this takes, is usually the same as just buying new cells or good batteries, so only do this if you absolutely can not get new cells, or if you can get all the laptop batteries for free.
The last tip is: Planning
Every time you visit a tower or an installation, is time wasted that you could have spent building a new one. If you do everything right the first time, it will save you a lot of time.