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Explaining Capacity of a Lightweight Lithium Battery

December 17, 2012

Last week I posted some basic thoughts about the use of Battery Tender® chargers on lithium batteries, and gave a few examples showing why this would not be a good idea. I also pointed out that several of our competitors claim that you can use a Battery Tender® on lithium batteries, or that this type of charger isnt ever needed.

I always laugh when I see, “No Battery Tender® needed!” as a selling point. If you don’t need one of these, should we just assume that your version of a lightweight battery simply never gets drained? Have you managed to produce a battery that is actually an unending reservoir of energy? Wow- awesome!

Or not. Yeah, actually not awesome. More like lies and obfuscation to sell product. Thanks guys- you are making everyone who produces lithium batteries look bad by association.

So, back to the Battery Tender® issue. What no one ever talks about is “why” you would would need a Battery Tender®, or maintenance charger. Lets quickly go over that question again, as it needs to be repeated. A good place to start is with an understanding of battery capacity.

Basics: a battery (any battery) is an energy storage device. A battery does not produce energy, it stores energy. In fact, every battery has a specific capacity, which should be easy to understand.

Unfortunately, battery capacity is another one of those areas- like charging of lithium batteries- where other companies are being less than honest about their batteries’ capabilities, and the methods used to rate them. In the case of lithium batteries, we now have every other battery company in the US using “PBeq” or some related term, to describe the capacity of their batteries. And as with the Battery Tender® issue, either these guys simply don’t know the truth, or they are lying to their prospective customers. (We will even supply you with a “PBeq” or “lead acid equivalent” rating for our batteries if you so choose, but we don’t believe it is at all accurate.)

Truth about lightweight battery capacity

We are very clear about our batteries’ capacity. We will even explain the methods which we use to determine capacity. We helped Motorcyclist Magazine to standardize their capacity testing earlier this year in an article about lithium batteries, which you can read here.
Here is how we rate battery capacity:

A 1 amp load/draw x number of hours= capacity (where voltage stays above 12.6v). Pretty complicated, right?
See, if we use this very simple method, everyone can understand it, and replicate the test with a light bulb and some wire. No fancy algorithms; no complicated math; no extrapolation based on lead acid stated capacity; KISS: Keep It Simple Stupid.

Further, we specify a 1 amp load because this is something that you are likely to see when you have an alarm or LOJACK on your vehicle, or if you leave your headlights on by mistake.
12.6 volts also makes sense as a threshold; while we could claim a much higher rating if we allowed the battery to go down to 3 volts, it wouldn’t do much good since your motorcycle, car, ATV, plane, whatever, isn’t going to work at 3 volts…so why bother with providing that rating?

Using this very simple method for rating battery capacity- which actually makes sense to people who actually use our products- we find that our numbers work. In the Motorcyclist Magazine article mentioned earlier, we sent them a battery that was rated at 4.6 amp hour. It was delivered to them at roughly 60% state of charge. When they tested all of the batteries using our method, they found that our battery provided 3.7 amp hours, and that was right in line with all of the rest of the batteries from other companies. Since we don’t ship our batteries fully charged- to comply with shipping regulations- the 3.7 amp hour figure is pretty close.

“Right in line”- even with the ones that claimed 15, 18, 21 amp hour ratings. The Chinese battery with the Prismatic cells which claimed to be 18 amp hour, tested to be less than our claimed 4.6 amp hour. How can this possibly be the case? Well, I have feeling that they are lying, in order to sell more batteries. Either that, or their battery does not perform as advertised, and didn’t live up to its stated capacity. I included a short discussion of these phony “PBeq” or “lead acid equivalent” ratings that other companies are using to lie about their batteries capabilities in our Pulse manual. You can download and read it here.

Back to “why” you would need a maintenance charger. If you leave your battery connected to your vehicle, there is a very good chance that your vehicle will eventually drain the battery, as I mentioned in last weeks blog post. Think about what happens when you leave the dome light on in your car for a few days- even with that massive lead acid battery which might claim to be 40 amp hour, it gets drained by one little bulb, and you need someone with jumper cables to start your car. Makes a little more sense now, right?

So, you need a maintenance charger for a battery for those reasons. It is fairly simple to understand when you lay out the numbers in a way that relates to the vehicles that actually use these batteries, isn’t it? So, while not every vehicle places the same load on a battery when it is turned off, many of them do, including all of the cars and motorcycles that I own personally.

YMMV.

I should point out that there are other ways to charge a lithium batteryfor use in a performance vehicle, besides a maintenance charge like the one we have discussed here. Many drag racers, land speed racers, and even some road racers, have vehicles without charging systems. For those people, a rapid recharge is required, and we have a solution with our CV1 charger.

Balance charging is also something that should be done with lithium batteries occasionally, or as needed, depending on the condition of the battery.

I am working on a post where we will discuss both of these options for charging a lightweight lithium battery.

Have a good week!



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