Question: What are the best batteries? How do you determine the right batteries to buy?

Submitted by Solar on Fri, 12/10/2021 - 14:17

There is no prefect scenario, there is only the batteries that serve the purpose.

Like good old fashioned carbon batteries for that toy you had in the 60s, only to be replaced by an alkaline, then rechargeable Nickle Cadmium (NiCad), then the Lithium, and lithium rechargeable, but each successive breakthrough came with higher costs until they flooded the Mkt. (a cycle is draining a lead acid battery below 70%. No, this is not a rule, but a guide, so so size accordingly)

Lead Acid, the same as you have in the car has been around for over 100 years, so they are the goto where cost is involved.

But even lead acid has differences, for example, telecommunication batteries, or what we called back in the day, railroad batteries. They were designed to sit for years until called upon.

They have a 20 year life, but the trade off is they are harder to charge after use, run them completely dead, and it could take days to bring them back if you haven't the ability to push high levels of current into them. These batteries have a higher cycle rate as well, but still, don't do it, the more you cycle a battery, the more you remove its ability for capacitance, till the day you cycle too much and it quits taking a charge.

But these batteries also come with a huge price tag if your requirements are heavy constant loads, like say a fridge or air conditioning.

The more you buy the more solar/generator power they're going to require. Example, if you only need enough for one LED light, and you have three times the solar array that the LED draws, your battery will probably last 20 years, all because you technically didn't cycle the battery.

Same rule applies to huge battery banks, you need in practice, three times the amount of input than the batteries store.

There are several reasons for this, but suffice it to say, this is not a plug and play operation, so you have line loss/friction/resistance, so wire sizing is extremely important, then there is the issue of chemical reaction, a loss of upwards of 20% off the top, as well as conversion through the inverting from AC to DC, more loss.

This is why you must decide at the start the size of your system and your budget because you only get one year to add batteries to your system, beyond that is like replacing all the batteries in your flashlight but one. So when buying batteries, decide ahead of time, what are your immediate needs and can I keep them charged regardless.

You could go with a bunch of T-105 cheap golf cart batteries, they're a bit cheaper, have a 7 year life and afford you a learning curve.

Orrrr, you could start with an off the shelf trolling battery or two, a cheap $30 dollar inverter from the same auto parts store and experiment before you jump in with both feet. Trolling batteries are a somewhat of a hybrid between a true deep cycle and cranking amp battery, not advisable for solar systems, they don't have a long life.

Getting back to what's the best all around battery? Well I really like the Trojan L-16, they're relatively easy to charge, take far more abuse than a T-105 golf cart battery or trolling motor battery, and if you never cycle them (more than 30% of the banks capacity) you will get more than 10 years out of them.

I have one customer call me 16 years later after having bought 24 L-16, they had finally seen their journey end. Keep in mind, this guy was frugal, only watched TV and had tiny RV lights, no real loads and a large solar array, even limited light in the winter kept his bank topped off.

There are other options, but unless you are a multi millionaire with money to throw away, Tesla may not be best for you. Personally, I'd love to experiment with Tesla's Power Wall, cycling it doesn't hurt it, you can completely drain them, or at least until the inverter shuts down, but in essence, you get a near 90% return on power, where a lead acid is closer to 60% and even then, damaging to the battery.

Oh, and stay away from using car batteries, you'll only get 3 years and they don't appreciate any form of cycling, meaning drawn down over night, they're designed to give up current on demand, but expect it back immediately in the form of a charge. You will not get 100 cycles out of one.

This is not a flaw, this is by design as In "Cranking Amps". Solar applications don't need cranking amps, just the size of the bank alone covers that issue.

You could do the weekender, I have a lot of customers that went that route. They'd get just enough power to last a weekend, they essentially abuse the batteries, leave and the solar array would charge them all week. Problem with this is, the bank will probably only get 4 years of use and have to be replaced.

Here's the thing, anything you do will work, the point is to do what works, ONCE!

The last thing you want to do is incur the cost of batteries within a few years, so build the biggest bank first, get a good diesel generator and charger, or inverter/charger, then slowly build your solar array.

All this, based on assuming you want to live off grid now. If you just want power backup, then stick with the 20 year battery.

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