Did You Know..why there is a C value or 20h indication on a battery?

[howson]

Fantastic video by Victron on the effect high (and low) discharge rates have on the different battery types:

My takeaway: if adding an inverter or something that will draw a heavier amperage load than as designed originally by GD, (inverter, etc), replace your lead acid with LifePO4 batteries.

I've added this info to the battery Reference Material post: https://gdrvowners.com/forum/operati...ithium-battery

[Guest]

I charge my lithium battery at 0.5C for longevity where its discharged at much lower C values, for now.

Jim

[howson]

I charge my lithium battery at 0.5C for longevity where its discharged at much lower C values, for now.

Jim

According to Victron, .5C is perfect, Jim!

[Guest]

Yes due to the Peukert law 0.5C is the best rate of charge. This law also is used to define the 20h metric where batteries can be compared. Lithium is a special case where its self heating will raise efficiency as defined from the Nernst Equation. I'm getting ready for my last boon docking trip where generator use will be minimized due to superior lithium performance. So nice.

Jim

[StephenO]

howson and Guest - is my assumption correct that by saying you charge at "0.5C", that is the amperage you are charging at? If it is, I'm also assuming that you would need to normalize the C AH rating listed on a battery to 1C, then divide by 2 to get 0.5C? For example, if the battery lists 200AH @ C20, you would charge at 5amps?

Is that correct, or am I way off in left field?

Thanks!

[ncitro]

howson and Guest - is my assumption correct that by saying you charge at "0.5C", that is the amperage you are charging at? If it is, I'm also assuming that you would need to normalize the C AH rating listed on a battery to 1C, then divide by 2 to get 0.5C? For example, if the battery lists 200AH @ C20, you would charge at 5amps?

Is that correct, or am I way off in left field?

Thanks!

Now you’ve got me thinking. I’ve always assumed it was the 200AH/2, or 100 amps charge max. In my case I’ve got four and I charge at 125 amps which I figured was close to .25C so I was good to go. Maybe I’m wrong though.

[Guest]

Battery capacity is determined and rated at 20 hours. C is the total capacity of the battery or battery bank. The 20 hour test is a way of normalizing every battery in what steady discharge current can be delivered over the standard 20 hours. So for a 100ah lithium battery the discharge test would be 5 amps for 20 hours as an example. 5x20 =100. So by adding batteries in parallel, your capacity is raised.
Two 100ah Lithium batteries in parallel will have a rated capacity of 200ah where a 10amp load can be applied over a 20 hour period which would equate to 200ah. Another way do this is to apply 200amps for one hour where the result will be approximately* the same. So for the two 100ah lithium batteries in parallel, the charge current at 0.5C would be 100 amps..

*Peukert's Law (also applies to Lithium)

Peukert's law, presented by the German scientist Wilhelm Peukert [de] in 1897, expresses approximately the change in capacity of rechargeable lead–acid batteries at different rates of discharge. As the rate of discharge increases, the battery's available capacity decreases, approximately according to Peukert's law.

[StephenO]

Battery capacity is determined and rated at 20 hours. C is the total capacity of the battery or battery bank. The 20 hour test is a way of normalizing every battery in what steady discharge current can be delivered over the standard 20 hours. So for a 100ah battery the discharge test would be 5 amps for 20 hours as an example. 5x20 =100. So by adding batteries in parallel, your capacity is raised.
Two 100ah batteries in parallel will have a rated capacity of 200ah where a 10amp load can be applied over a 20 hour period which would equate to 200ah. Another way do this is to apply 200amps for one hour where the result will be approximately* the same. So for the two 100ah batteries in parallel, the charge current at 0.5C would be 100 amps..

*Peukert's Law (also applies to Lithium)

Peukert's law, presented by the German scientist Wilhelm Peukert [de] in 1897, expresses approximately the change in capacity of rechargeable lead–acid batteries at different rates of discharge. As the rate of discharge increases, the battery's available capacity decreases, approximately according to Peukert's law.

Interesting stuff, thanks! Coming from a world of discrete electronics, anything over 1 amp was crazy, so seeing your 100amp charging makes me cringe - lol

[Guest]

StephenO I went back and added in the "lithium" verbiage since FLA batteries would be charged at a different rate. I have a single 100ah Lithium battery and have targeted a 0.5C rating (50 amps) which is a reasonable charge rate while not reducing battery life. This past week the wife and I were boondocking where I would fire the generator at 9:00am to make a pot of coffee. In the time it took us to consume the pot of coffee the battery was charged and would provide power for the entire day with heat on and also through the night. Each morning I would check the battery SOC which was at 47%. A pot of coffee later and the rig was ready for another 24hrs with no generator usage. So nice!

Jim

[StephenO]

StephenO I went back and added in the "lithium" verbiage since FLA batteries would be charged at a different rate. I have a single 100ah Lithium battery and have targeted a 0.5C rating (50 amps) which is a reasonable charge rate while not reducing battery life. This past week the wife and I were boondocking where I would fire the generator at 9:00am to make a pot of coffee. In the time it took us to consume the pot of coffee the battery was charged and would provide power for the entire day with heat on and also through the night. Each morning I would check the battery SOC which was at 47%. A pot of coffee later and the rig was ready for another 24hrs with no generator usage. So nice!

Jim

That's a really good reminder to put out there, always read the spec sheet for your equipment and make sure you are within those. For example, the specs for my 6V AGM batteries say a maximum charge current of 30A, while their line of Lithium batteries say max current of 100A.

And BTW - I am super jealous of your Lithium battery capabilities! Maybe time for an upgrade :P

[ncitro]

That's a really good reminder to put out there, always read the spec sheet for your equipment and make sure you are within those. For example, the specs for my 6V AGM batteries say a maximum charge current of 30A, while their line of Lithium batteries say max current of 100A.

And BTW - I am super jealous of your Lithium battery capabilities! Maybe time for an upgrade :P

Yeah I have to agree with Jim, I run four Lion Energy Lithiums and the charge rate is insane. It is so nice to just need to run the generator for a bit in the morning and a bit in the evening to be topped up (assuming its cloudy and I need to run it all lol). I know they are a ton of money, but they have been a delight. Able to use the full capacity of the battery, charge rate, maintenance free, and weight is an unbelievable combo.

[howson]

And BTW - I am super jealous of your Lithium battery capabilities! Maybe time for an upgrade :P

Well worth it if the budget will allow. I am a "super fan" of the LifePO4 (Battle Born in my case) batteries powering my trailer.