Originally Posted by JMF
Our Siesta has two Powertron house batteries joined in parallel. There is no Amphour rating on them - only 600CCA, 160RC and 750CA. Need to know the Amp Hours for 20A rating to set the Battery Monitor. Does anyone know this? I've seen several calculations on the web but they range from 67 - 82 AH for one battery, couldn't find anything more specific.
The 67 Amp-hour comes from 25 Amps X 160 minutes (2 hours 40 minutes), or 25X2.667. However, that’s discharging much faster than at 20-hour rate.
Your battery is listed as a “starting” battery, which typically don’t have 20-hour capacity ratings. I think you may not find the definitive answer you’re looking for.
I looked for another “deep-cycle” Trojan battery with similar 25-Amp Reserve Capacity of 160 minutes, and could only find an AGM deep cycle battery rated at 158 minutes and 89 Amp-hours at 20-hour rate. If you could extrapolate, it would place your battery “around” 90 Amp-hours at 20-hour rate. But you can’t really compare AGM versus flooded, or deep cycle versus starting all that accurately, so the 90 Ah is only a rough approximation.
If you find out from Trojan, please let us know. It will be interesting information to have.