Here is the battery (two used in-line):
Fully-charged / After 10-minutes of use:
Is this the normal drop in voltage after 10-minutes of use?
Are the batteries new? 11.75V is not a fully charged gel-cell. And if you’ve discharged to 9.21V it is likely damaged. Also, what were the batteries hooked up to? The case of the battery says it only supports up to 1.05A, you’ll easily exceed that if this was hooked to thrusters.
3.5Ah isn’t a very high capacity. I’d expect that to be normal if driving at T200 at full power.
As @spotxuv mentioned, its not recommended to discharge a lead acid battery below 10.5V: Reliable Power Converters and Battery Charging Systems
Yes the batteries are new. Good lead-in to why I posted this. I am replacing the batteries for the line-trimmer. But they only ran the trimmer of 10-minutes. I am trying to learn what what facts I can use to communicate with the folks I purchased the batteries.