“Low Battery” on Medallion display at startup.

[Chuck Jackson]

Whenever I start my coach, I turn on the key and let the relays do there thing before actually starting the engine. When the relays finish clicking, I get a display on my Medallion that says “Low Battery” until the engine starts. I always thought this was strange since I was either plugged into shore power or had been driving so I knew the batteries were charged. Today, I cleaned my engine and as usual, I tend to get the serpentine belt wet. When I started the engine, the “Low Battery” message stayed on longer and only went out when the wet belt stopped squeaking. So I’m wondering if this message is tied to the alternator output rather than the battery condition. Could this be the case?

[Mike Shumack]

It is my understanding that the Medallion voltage reading is coming from a connection at the batteries. So after you crank the engine, the battery voltage is drawn down. Once the engine starts the alternator charges up the batteries again, as you noted.

I think either the alternator is not charging fully (slipping belt or weak alternator) and/or the batteries are getting to the point where they don't hold a full charge and discharge faster than then they should (faster than new batteries would) while a load is on them.

You can test this with a voltmeter.  You should be getting around 12.5 to 12.7 volts at batteries with engine off. Then start the engine and see if your getting 13.8 - 14.2 volts at battery.
If the voltage is lower than 13.8 ish when running, then measure at the back of the alternator (to run out a bad/loose cable). Also check the condition of the battery cables.

If the batteries are just old and weak/sulfated, it's hard to test at home, you really need to have them tested at a shop (or buy a battery tester).

[Chuck Jackson]

Hi Mike,

I'm seeing the "Low Battery" message from a fully charged battery (according to my Magnum controller display and being plugged into shore power for several days/weeks) and have not cranked the engine yet. I *think* my batteries are ok since I just did a week of dry camping and my voltage only dropped to 12.2 overnight. Except for the message, all seems fine otherwise. I'll check the voltage at the batteries to be sure. Maybe when the coach battery charger says it's charged (13. it's actually right at the low end of being charged and it triggers the message.

[Mike Humble]

Chuck,
I get the same low voltage reading on our C-15 with brand new batteries.  However never saw it on the C=9s.  I have been told it is normal.
Mike

[Steve Huber Co-Admin]

I always use the boost switch when starting the engine and the generator to reduce the draw on one of the  battery sets.
Steve

[Fred Cook]

 Could be a sign of an alternator going bad. I always had to use my boost switch...  until I changed my alternator out... now I don’t need the boost switch anymore.  My alternator was the original from 2001 and I did not want it to fail somewhere on the road.