Not familiar with Newmar's. Does the Salesman Switch not turn off your Magnum too?
These are obviously wet cells, so I'd suggest reading Trojans site on tips of maintaining, and equalizing.
If you have stand alone Battery Charger with Equalizing capability, this could be the safest way for you to go until you get up to speed on the Magnum in your specific coach. Maybe borrow one from a buddy if you don't have one(?). This would allow you to disconnect the battery cables, and just let the Equalization process do it's thing:)!
-Fully charge the batteries before Equalizing
-Follow your specific batteries recommendations for Equalizing. If it's a battery that does not provide this kind of technical data. Then I'd suggest Trojan's as I feel a good process for wet cell batteries.
-If the batteries give you and indication of being heavily sulfated. Then I'd do the the following too:
-Drain the batteries down say 65-70% SOC
-Fully charge them again
-Equalize the a second time
(The second Equalization, maybe enough to help break away some of the sulfated build up.)
And if those are OEM, don't be surprised if these steps do not recover the battery to useable condition:)!
Best to you,
Smitty
(Just lost a Chassis CAT 8D Maintenance Free after 6 years of usage. My bad, as we'd abused it running it down too low at least 5-6 times. Usually caught the problem quickly, and got it charged back up quickly too. Think the last time was too long... DW was dusting the coach, and turned on the Fog Lights, did not find it until two days later... So it had sat drained for probably 32-38 hours before I restarted the charge process. Did the steps above, but still had two cells that were too low to keep the battery for starting duty:)!)
