Thor Siesta Mercedes Chassis Battery drain

JMF · 10-28-2019, 10:10 PM

We have just replaced our AGM Battery (80Ah) with a brand new one, since the old one was discharging within 6 days and appeared to drop charge under a small load.

We charged the new battery fully and then tested every day to see whether it was maintaining its charge. The main house switch is off and there doesn't appear to be any other load on the vehicle.

Here's the result: We are losing about 0.5V every day. It started at 12.8V and is down to 12.4V after 6 days (52%).

Has anyone else had this problem and resolved it? I've researched this on the web - seems that some people resolve it by using a Trickle Charger from the House Batteries, but I'd prefer to find out what the source of the drain is.

Any ideas?

Bob Denman · 10-28-2019, 10:17 PM

Why not throw a battery disconnect switch into the mix, and see if it helps?
This is what I did with mine...

Okay: I ended up putting two on the battery bank. I wanted to completely isolate them.

http://www.thorforums.com/forums/att...1&d=1572301064

JMF · 10-29-2019, 12:23 AM

Quote:

Originally Posted by Bob Denman

Why not throw a battery disconnect switch into the mix, and see if it helps?
This is what I did with mine...

Okay: I ended up putting two on the battery bank. I wanted to completely isolate them.

http://www.thorforums.com/forums/att...1&d=1572301064

We can disconnect the chassis battery by pulling the plug by the gas pedal. That fixes the drain when storing the MH.

The main switch is off for the house. But there shouldn’t be a big drain on the starter battery when.all systems are switched off.

Gebills · 10-29-2019, 04:03 AM

I have a 2018 Thor Synergy on a 3500 Mercedes chassis. When the motorhome is not in use, I store it in a covered storage area without access to 110 V. If I pull in to storage with the battery fully charged, i.e. 13.2 volts, it will take roughly 5 to 6 days in storage and the battery will be below 12 volts. My only way to charge it has been to start the coach Onan generator and charge the chassis battery with a small 6 amp charger. This of course takes propane, time, much patience and adds lots of hours to the generator. After following some of the forums, I have ordered a 18 W solar panel/trickle battery charger today from Amazon. I live in southern Arizona so I have lots of sun to charge the battery with. The afternoon sun shines in on the front of the cab even though it is undercover and it will provide adequate sunlight on the solar panel to keep this battery charged. I had never thought about the recommendation of putting in a couple of knife switches that was mentioned above; that’s not a bad idea either. After owning this rig for about 17 months, I’ve found that this parasitic drain is common, and did not surprise the Mercedes service advisor when I ask him about it. I guess it’s just something that we will have to live with, be that through adding some sort of trickle charger while the coach sets idol, or put on the knife switches and disconnect the power totally. I suppose this is a small price to pay for, in my opinion, an excellent chassis, particularly this Mercedes diesel.

JMF · 10-29-2019, 12:23 PM

Hey Bob, Did you have a chassis battery drain and if so, did it fix the problem ?

Bob Denman · 10-29-2019, 01:11 PM

I did...

Based upon my experience with our Outlaw: I felt it was easier to just completely isolate the batteries.

lwj · 04-28-2021, 03:23 PM

So I have been experiencing the same battery drain issue with my Thor Synergy on a Mercedes Sprinter chassis. The local Mercedes dealer service department couldn't find the source of the drain, nor did they mention the battery cable disconnect located above the foot pedal. I suspected the source of the drain might be the Axxerra radio, confirmed by some threads on this web site. So I called Axxera radio tech guy just confirmed that the radio which Thor installed does in fact drain the battery even when appearing to be "off." He suggested I install a toggle power switch connected to the red wire located behind the radio. He said I could easily remove the radio by prying off the border trim, then sliding some knives down the sides to release the clips. Then cutting the red wire and installing the switch, locating this switch to somewhere handy. Inside the cigarrete tray? I haven't tried this yet. Has anyone else? News to follow.

Bob Denman · 04-28-2021, 03:35 PM

If your "Use/Store" switch is turned off: there's no power to the radio anyway...

Dick1030 · 10-17-2021, 04:33 PM

We have a 2019 Thor Siesta Sprinter on the MB chassis. When plugged into shore power, it will not charge the chassis battery. We had the same problem with our 2000 35' Winnebago Adventurer. There are always some drains on the chassis battery that you are unaware of. It is best to disconnect the chassis battery when you are on shore power for a few days unless you have a trickle charger from the house to the chassis batteries. That is what I intend to install, since I just had to jumpstart our Siesta because I forgot the disconnect when we were on shore power for a few days. Just be sure to get one with some kind of controller to prevent overcharging.

HarryTh · 10-18-2021, 04:49 AM

I have a 2008 Sprinter. I have 2 group 31 AGM batteries for the house. I under the hood and one in the compartment after the side entry door under the sink and cabinet. The engine has a jump point under the hood. I made a short jumper cable to go from the house battery under the hood to the jump post. I hook it up if I am not using the coach for more than a week so the converter will keep house and engine battery charged and unhook it when moving the coach again. If you do manage to kill the start battery or the house battery you can hook it up to start the engine or the generator depending on which one died. Works for me.
Harry

racefan · 11-07-2021, 09:03 PM

I have a 2018 Freedom Elite 24FE on a Sprinter chassis.(7500 miles on it) Yesterday when I tried to start it the battery was dead. It’s been sitting for 5 weeks with the battery disconnect down by the throttle pedal disconnected. There shouldn’t be anything draining the battery as long as that’s disconnected should there?

Beau388 · 11-07-2021, 11:35 PM

Quote:

Originally Posted by racefan

I have a 2018 Freedom Elite 24FE on a Sprinter chassis.(7500 miles on it) Yesterday when I tried to start it the battery was dead. It’s been sitting for 5 weeks with the battery disconnect down by the throttle pedal disconnected. There shouldn’t be anything draining the battery as long as that’s disconnected should there?

The self-discharge rate for a flooded lead-acid battery is about 5% per 30 days, if the battery is new. The self-discharge rate will increase as the battery ages or is damaged by over discharging. There is parasitic battery draw on a chassis battery if left connected, as the radio, engine computer and transmission computers have volatile memory that requires keep alive current as does any clock. Any remote control device (remote door unlock, remote engine start, etc) will draw current continually. That said, any flooded battery that is the size recommended for the vehicle, should maintain sufficient charge to start the vehicle after 60 days of no use. If it doesn't have enough capacity to start the vehicle after 60 days of no use, have your battery tested and if it tests good, you have an abnormal battery drain.

JMF · 11-08-2021, 12:04 AM

We have a Thor Sprinter Siesta. When the battery is disconnected by the gas pedal it loses very little charge. When the battery is connected there is a drain.

I'd get the battery tested; sounds like its not holding its charge even without a load on it. Having said that, batteries should be trickle charged occasionally to keep them in good shape.

Secondly, if you have a solar charger (20W) that can plug into the live cigarette lighter (the lowest one) this can provide enough charge to keep the battery healthy (depending upon the weather). When on shore power I usually plug in a battery tender which keeps the chassis battery fully charged.

racefan · 11-08-2021, 12:10 AM

The battery disconnect was disconnected so there shouldn’t have been a drain. It only had 1289 miles on it when we bought it at the end of April. I suspect maybe the battery's sat too long not being used. I took it to a Sprinter dealer in July to get serviced,they tested the battery and said it was good but I’d driven an hour to get there. I reckon it’s new battery time.

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