Maintenance, Troubleshooting


Will the Roadtrek E-trek solar panels keep the batteries “topped up?”

In our previous post from mid-June, Our 2015 Roadtrek E-trek (What we have learned) we promised to provide some follow-up testing regarding the charging for the Roadtrek E-trek batteries by the various methods: driving, idling, solar panels, and plugging in to shore power.

Roadtrek has clarified the following terms, which appear in the Roadtrek E-trek Owner’s manual:

  • Full charge…..25.5 volts
  • Moderately depleted…..24 volts
  • Adequately charged…..23.5 volts and above
  • Minimum charge ……21 volts

According to the E-trek Owner’s Manual, the Roadtrek E-trek solar panels are supposed to keep fully-charged batteries “topped up.”  To do a fair test, we wanted to start with fully charged batteries. Also, anything that drains the battery (battery disconnect, Webasto, and inverter) needs to be turned off. During the test, we only turned on the inverter briefly to check the battery reading.

Before plugging in to shore power, the battery strength was 90%/25 VDC (VDC=Volts DC); according to Roadtrek, 25 Volts is considered “adequately charged.” On Tuesday, August 4th at 8:00 AM, we plugged into (20 AMP) shore power. Remember,  in order to charge the batteries off of shore power, set the inverter to the “up” position, i.e, Power Saver Auto.  You should see the “battery charger shore power on” light illuminated (see photos below). Also, note that when plugged in, the battery strength goes to 100%/27VDC.

IMG_5023   IMG_5024

After one hour, at 9:00 AM, we disconnected from shore power and checked the Roadtrek E-trek battery reading, which was at 98%/26VDC, which is considered “fully charged” by Roadtrek.  We plugged in to shore power again and checked the readings hourly. (Each time we checked the reading, we first disconnected from shore power, because the battery will always read 100% when you are plugged in to shore power.) At 10:00 AM the E-trek battery strength was 98%/26 VDC, and at 11:00 AM,  the E-trek battery strength was 100%/27 VDC.

At 11:00 AM we disconnected from shore power and continued to check the readings to test whether the solar panels maintained the battery strength. At 1:00 PM the battery strength was at 95%/26 VDC. At 2:00 PM the battery strength was at 94%/26 VDC. By 6:00 PM the battery strength was down to 90%/25 VDC.

Conclusion: According to our analysis, the solar panels do not keep the batteries “topped up” since 25 VDC is not considered fully charged.

Our next test will be to see to what level (in volts and percentage) the solar panels can recover the batteries after being run down to 23 volts (68%).


  1. Thanks for the update.

    At 1PM and at 2PM, what was causing the battery drain? Did you have any devices running? I know that the inverter uses some power but were you running any equipment? Plus, as you mentioned, the solar panels should have kept the battery ‘topped off’.

    Looking forward to your response!

    1. No we did not have anything running. The battery disconnect, Webasto, and inverter were turned off. We only turned on the inverter to check the battery each hour. We have concluded that the batteries deplete even if nothing is running and the solar panels can only return them to a level of 87%/25 VDC. Please see our latest posts for an update to our testing which led to another service appointment at Mercedes-Benz.

  2. How long does it take to fully charge a dead battery when plugged into shore power at home?

    Also, when at home and plugged into shore power, did you upgrade to a 30 amp outlet? Or are you plugged into a standard 15 or 20 amp outlet.

    1. We have never plugged into shore power with a dead battery–usually it is at about 85%. From that point, it only takes a few hours to charge using 20 AMP. If you are starting with a depleted battery, you would have to allow at least overnight and maybe longer at 20 AMP. We looked into 30 AMP, but our electrician wanted $400, which seemed a bit steep. The outlet in our garage is 20 AMP and it seems to work fine.

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