Last week I backed out the motorhome onto my drive to flush out the hot water tank and drain the freshwater tank. I used the boost switch and it started right up. After around 2+ hours, I attempted to restart the engine using only my starting batteries, 2-Optima Red Tops purchased March 2020. They seemed too weak to turn the engine over, so I used the boost button to start the engine. I then removed the batteries and hooked them up separately/one at a time, to an "Optima Digital 400" 12V Performance Maintainer and Battery Charger. Each were brought up from 75% to 100%. No faults of error messages were noted. Each were floated at 13.4 volts for 12 hours. Then I disconnected the charger. After another 24 hours, the batteries are down to 12.8 volts (with nothing connected to them). Are the batteries failing?
Side question: any reason to place the batteries on wood vs concrete while I wait?
Thanks
Bob
Nothing wrong with your batteries fully charged sitting is 12.7 to 12.8 the old rule of concrete draining batteries is no longer an issue due to the newer components.
Anything above 12.6-12.8 volts on a lead acid battery is just a surface charge. The only real way to determine the condition of you batteries is to have them load tested.
Thanks for your responses.
Bob
I just went after a fix on this issue my self last month ( always requiring couch batteries to assist starting).
Step one: cleaned ALL cable connections. from engine block ground strap, solenoid, starter, terminals and posts. wire brush and flat file until all surfaces are bare shinny and grease free.
Step two: My cummins 450hp starter optimum cranking amps is 950. yet the four 1000 amp starting batteries that all tested to be putting out 910 to 925 would not roll the engine over sufficiently. The batteries are wired in series with one cable running from batteries to distribution terminal. It was pointed out to me that this a poor design. All the batteries energy was being compromised at each connection and unable to be sent on via one down stream cable. The fix. I added and additional Pos. and Neg. cable from the opposite end of the battery series wiring to the distribution terminal.
Result, the engine starter now spins like a top! Good luck, ALWAYS work safely Under the lifted motor home! Kind of wordy here I don't know how to add photo. Yet