We have 2 6v deep cycle batteries and a 2500w LP Onan generator. About how long will we need to run the generator to recharge the batteries from "empty"? We usually keep the batteries charged with daily driving. However, this last trip was spent with several days parked with no hookups. We ran the generator to recharge the batteries. We are thinking that maybe the control panel which shows the charge of the battery gives inaccurate info. The control panel showed the battery charge as "full" after running the generator only about 30 minutes. The battery indicator read "empty" by the next morning with minimal usage (refrigerator on propane and LED lights and movie for about two hours). We tried running the generator again for 30 minutes, the indicator again read "full", but over the course of about three hours the indicator dropped down to empty.We are guessing that the batteries really aren't full after running the gen for such short time and that for whatever reason, the indicator panel can't be used to judge how full the batteries really are after running the generator?????We need your expert advice! Thanks

Charging batteries have a curve, and depending on your RV's converter, 30 minutes likely won't add much. You likely will have to run the generator at least for a few hours to get back to a decent charge level (~60%). To get back to 100%, it will need to be plugged in to shore power for a day or two.The indicator will read "full" when the generator is on, and briefly afterwards. Then it will drop back to the "real" value. That is normal.The indicator lights are OK, but I personally recommend installing a voltage readout (Trimetric is the best brand for this), so you know exactly where you are, and not relying on a set of idiot lights.

Even with an excellent converter to do the charging, it will take 2 to 4 hours to charge a low battery to 90%. Another 6 to 8+ to get 100%.You need to be charging in the 14.3 - 14.8 volt zone for a fast recharge. Most oem converters charge slow at 13.6 volts.The indicator just shows the instant voltage is above 12.6 and calls it full. It is not full in 30 minutes.You may want to upgrade your converter. Post what you have for best recommendations. If you will be doing this off-grid camping more in the future consider 100 watts to 250 watts of solar.

Buy a good battery charger and plug it in while generator is running.Will significantly reduce charging time but you may have to replace batteries a little more often.Also check electrolyte levels at least monthly.It is what I do and I have had no adverse affects

Hi Since you are in a 2012 RV you may have a 3 stage converter. But--we need to know the make and model to give better advice.

Our converter is a Parallax 7355

Recharging house batteries with generator | Good Sam Community

17 Replies

mlts22
Explorer II
Feb 19, 2014
JamesJudasPriest wrote:
I just can't believe they are still putting in******single stage converters in motorhomes in 2012. It's almost an insult to the folks who have spent 100 grand only to find the manufacturer wanted to save 90 dollars for a critical part of the electrical system.

I've seen a couple class "B"s and "C"s that have single stage converters in them. One RV dealer I was talking with has offered to toss in a Magnum Energy MMS-1012 (four stage charger with temperature gauge and 1000 watt PSW inverter) as an upgrade from the single stage junk that comes with the rig, and I consider going with at least a three stage converter the minimum these days.

I'm guessing because most people don't know, and perhaps don't care (since they go from hookups to hookups), but for those who spend time dry camping, a single stage converter is a battery killer.
pianotuna
Nomad III
Feb 19, 2014
Hi SMK,

Fixed voltage only works when temperatures are not too hot, and not too cold. I saw 15.3 volts from my solar yesterday @ 3C (37.4 f). This in spite of the 13.6 that my converter has been pumping into the battery bank for a month!

smkettner wrote:
Yes with a generator installed there should be a better converter. Or have an off grid option with better charging. Fixed voltage is only fine driving to a destination and plugging in for a week.
time2roll
Nomad
Feb 19, 2014
Yes with a generator installed there should be a better converter. Or have an off grid option with better charging. Fixed voltage is only fine driving to a destination and plugging in for a week.
JamesJudasPries
Explorer
Feb 19, 2014
I just can't believe they are still putting in******single stage converters in motorhomes in 2012. It's almost an insult to the folks who have spent 100 grand only to find the manufacturer wanted to save 90 dollars for a critical part of the electrical system.
1775
Explorer
Feb 19, 2014
My Roadtrek has an Onan 2800W generator and a Tripp-Lite inverter/converter/charger. I have two AGM coach batteries. It takes 12 hours plus of being plugged into shore power to charge the coach batteries. I exercise the generator for two hours each month and in that time the batteries get little charge. There is no way that running the generator for thirty minutes is going to charge the batteries.
time2roll
Nomad
Feb 18, 2014
^^^ you really do need a three stage converter to properly charge and float an AGM.
Lifeline, Trojan, Universal all make a group 27 AGM for direct replacement.
SBradley
Explorer
Feb 18, 2014
Pleasure Way Plateau TS 2012.

Question:
Does anyone know the manufacture/model # of the Power converter?
I live in Alaska and store my toy in the lower 48, so I can't check for myself.

I know the house battery is an Interstate SRM-27, it is suppose to be a deep cycle battery, but I checked the web and can't find anything that says it is an AGM, only found wet cell for that battery. I would like to convert to AGM but need to know if the converter will charge it properly.

Thank you,
Bradley
Fastpaddler
Explorer
Feb 18, 2014
I too have found that running generator for an hour only partially re charges the deep cycle battery(ies). House power charging(shore-power) for a day is best in MY experience. I take mine for a drive in winter to generally exercise my little camper! Engine alternator charges faster than genset. I never leave house batteries to deplete fully. Deep cycles recover somewhat better than the engine battery--I have a solar 12V trickle charger on that. The Ops newish rig is more modern than my 'old' 06 PW Plateau TS. Don't go 'charging' off on a trip with a dead battery, please!!!
pianotuna
Nomad III
Feb 17, 2014
Hi,

The Parallax 7355 would take about 40 hours of generator run time to reach 90% state of charge. If the bank were at 50% state of charge it would take approximately 23 hours of generator run time to get to 90% state of charge.
Handbasket
Explorer
Feb 17, 2014
If you've been running down to 'empty' very often for very long, your batteries may be suffering. Google "12V Side of Life" to learn much more; every RV'er should read & bookmark this site. Generally, running them down below 50% shortens their life, but what 50% is is a whole deep subject. As said, the indicator lights are a pretty darn poor judge. Get thee to Cramping Wirld and bring back at least a 12V meter that plugs in to a lighter socket.

Jim, "Puritanism: the haunting fear that someone, somewhere, may be having fun."