BATTERY BASICS - Battery Capacity Explained - Understanding Amp Hours, C-Rate, 20 Hour Rate & More 

It can do it, but keep in mind that you will sacrifice some cycle life to do so. See if you can find more information from the manufacturer. Many of the top manufacturers will publish a chart that shows cycle life vs depth of discharge and that can help you make a decision on how much capacity you should plan to use each cycle before recharging to get the length of service you want.

For lead acid, you can't interchange the rates like that. It will give you a ballpark estimate, but there is a law called Peukert's Law that states that the more current you draw, the less overall capacity you will get out of the battery (lead acid). So you will get less overall Ah out of a battery at the 10 hour rate than you will at the 20 hour rate. So you can do the math like you were describing but just understand that your numbers will be off and sometimes way off.

@LDSreliance Thanks, I suspected that might be the case. Clearly, the relationship is not linear.

No, it is not. That is why they have different hour ratings. Some manufacturers are better at publishing the rates than others, unfortunately.

@@LDSreliance So true! I recently learned of Trojan batteries. Wish I had known of them before I bought the Duracell deep cycle batt I have. Trojan Ah specs are the most complete I have seen. I am looking at a Trojan, group 31, lead acid, AGM deep cycle batt and this is what they publish for Ah capacity: CAPACITY AMP-HOURS 5-Hr Rate / 83 Ah 10-Hr Rate / 92 Ah 20-Hr Rate / 104 Ah 100-Hr Rate / 115 Ah Tells the whole story! No "hide the weenie" like most manufacturers. Lets you easily compare their specs to other batts, whatever Ah rating is given!

You can exceed the 25A. Lead acid batteries can handle high current, usually. But the voltage will drop significantly and you won't get anywhere near 100Ah at 25A. Maybe 70Ah if you are lucky.

Yes.

Thanks, David

At 500W you would have roughly 21 hours of run time. But that doesn't take in to account real world conditions so lets say about 20 hours. If the load averages 350W then it would be about 30 hours or probably about 29 in the real world. However, if your inverter is not very efficient at lower loads then it would be lower than those numbers.

Worth checking!

There is no real limit to how many batteries can be connected to an inverter. But for practical purposes you would be limited by the space you have available and your budget. 7 days of battery power is almost impossible unless you have a LOT of money to invest. Even fans and small devices add up if they run around the clock.

@@LDSreliance Thanks have some space and a little money to improve storage of the sun, when it shines...Good videos very informative.

Thanks! I appreciate that. Good luck!

I wouldn't say it needs changing unless it never gets above that point. A fully charged flooded lead acid battery should be 12.6V when fully charged (after letting it rest for a while after disconnecting the charger). A fully charged sealed lead acid battery would be 12.8-12.9V at full charge.

Not really. The 7Ah battery would be rated at 0.35A for 20 hours. It would also be able to supply 1A for 7 hours, roughly speaking. The Peukert Effect would be negligible at 0.14C. Maybe the difference of 10 or 15 minutes, at most. I did explain C-rates and 20 hour rates if you watched past that point in the video.

@@LDSreliance I've never seen what your saying hold true in real world tests. At a 1C rate you are going to get far less than the 7ah rating of most lead acid batteries. Agree to disagree based on real world testing and research. We are only talking lead acid here.

But a 1A draw is nowhere close to 1C. It is .14C, like I said. The difference between 0.05C and 0.14C is negligible. You don't have to believe me. Look it up. Using 1A for 7 hours is a heck of a lot easier for people to use as a measuring stick than trying to figure out what 0.05C of 7Ah is. And the 20 hour rating essentially means nothing because no one draws such a tiny amount of power. 350mA @ 12V is 4W. That is probably less than the idle consumption of any inverter you would have connected to it. So it is meaningless.

@@LDSreliance 1 amp for 7 hours is 7 amp hours, Yes. I just so happen to have a 7ah battery on the test rig that gets 7300 mah at a 20h rate. I'll test it at a 7 hour rate (1 amp) and see where it lands.

@@LDSreliance Test results in, I was a bit off in my original number as I realized I had run my first test at 450ma which gave me 7368mah, the test that just finished was run at 1 amp and resulted in 6648mah. So OK, not as drastic as I mentioned, but still noteworthy. It's also not a linear slope of degradated returns, so a 2 amp test for example would be much more drastic. If I had tested at 350ma vs 1 amp the numbers would have been further apart. I'm going to just leave it at we are both somewhat right.

Except that is false. That is a commonly held false belief that applies to car batteries but not deep cycle lead acid batteries.

@@LDSreliance Tell Trojan. I just pull the info off their data sheets

Link me to that. All the cycle life charts for Trojan that I have seen show no dropoff at 50%. Nor does their literature say anything about permanent damage. In fact, they rate their batteries to a specific cycle life @ 100% DoD.

Why do you say that?