How to tell if your batteries are damaged

[dhurtt]

I bought a used RV last year and before the big trip last month I took it into the shop to have it checked over and have the water pump replaced. Before that we found that the RV, although it looked fine, it did seem to be a little worse for wear. (All the tires had to be replaced as they were blowing one after another.) So, when the mechanic said the house batteries needed charging "because they were dead", it didn't really click. If they needed replacing, I figured he would have tried to sell me some. The one thing he said that didn't get fixed was the "pulley needed replacing" and that part needed to be ordered. (This is a Mercedes Sprinter chassis.) Again, didn't really click in my head because I explained I was going on a several thousand mile trip and he did not warn me against it.

Over the course of 12 days, we had some electrical problems – indicators on the dash indicating that I had low battery voltage that would go off after a while – but nothing seemed off with the house batteries until the last 2 nights. I was plugged into shore power and the next morning, after unplugging, I noticed the house batteries were listed as empty. I figured that I had forgotten to switch the battery disconnect from Use to Store, so they had not gotten charged. The next night I made sure that I flipped the switch, but after a full night on shore power the batteries still showed they were dead. I have now been home for several weeks and the batteries are still showing dead.

So, I am trying to get an idea of the problem before I take it to the shop. 

1. How can I determine if the batteries are shot (damaged beyond use)? I have no idea how the previous owner treated the rig. I was plugged into shore power since I have owned it and only one night on the trip did I not plug in nor run the generator (and we only ran a single fan on low speed).

2. How can I determine if the inverter/charger is not charging? I don't want to replace the batteries and then they discharge below 50%, causing them to be damaged.

3. The mechanic said it was the "pulley". When I asked did he mean the belt he indicated no, it was the pulley. As he could not get the part before the trip, I said I would replace it after the trip, but he never ordered the part so... Isn't the pulley a part on the alternator? If so, could that be the issue with not recharging the house batteries and potentially why I got low-voltage indicators on the road (which, I assumed was the car battery)?

Just trying to sort things in my mind. I don't expect to fix it but I would like to understand better what is (and isn't going on) so I might tell if a mechanic is trying to pull the wool over my eyes.

This time I am getting serviced at the Mercedes-Benz dealer rather than the local RV place, who I have not heard many good things about.

Thanks in advance for any knowledge you can pass along, even if it is understanding the right questions to ask.

 

[highdesertranger]

I wonder what pulley they are referring to, idler pulley, tensioner pulley? if it was either of those 2 I can't believe they sent you down the road.

this goes for everybody. when a shop tells you something is bad, get specifics and ask them for a part number.

you need a multi- meter. everyone should have one. take a voltage reading with everything off. then start the engine now take another reading. now turn the engine off and start the generator, take another reading. shut the generator off and plug in.

with nothing is on the battery should read around 12.7.
with the engine running it should read between 13.8 and 14.4
with the generator running or plugged in the readings should be the same 13.8-14.4

highdesertranger

 

[dhurtt]

I wonder what pulley they are referring to,  idler pulley,  tensioner pulley?  if it was either of those 2 I can't believe they sent you down the road.

this goes for everybody.  when a shop tells you something is bad,  get specifics and ask them for a part number.

you need a multi- meter.  everyone should have one.  take a voltage reading with everything off.  then start the engine now take another reading.  now turn the engine off and start the generator,  take another reading.  shut the generator off and plug in.

with nothing is on the battery should read around 12.7.
with the engine running it should read between 13.8 and 14.4
with the generator running or plugged in the readings should be the same 13.8-14.4

highdesertranger

Yeah, I feel stupid for not asking. I was so focused on going on the trip it could well be that he did not want to tell me that I should not be going on the trip because I did not prepare adequately. As for the generator, it appears to use the house batteries as its starter, not the car battery, so it will not start.

I put a standard car battery charger on my house battery and got a fault error, indicating that it was not connected properly. It is appears wired in series, so I was unsure how to connect or even if a standard battery charger could be used. I am not thrilled about disassembling the whole thing and charging them one at a time and then reassembling them.

Thanks for the advice. I am scrounging for my multimeter. It is packed away somewhere in the house.  :-/

 

[jimindenver]

This is a simple test. Put a charger on the house battery or plug in the RV and if the battery's voltage goes from low to high quickly, it is not a good sign. It should take a while to get the voltage to come up. Likewise if you have been charging the battery and its voltage has held high for a while and you put a decent load on it only to have the voltage drop like a rock, it isn't good either.

Leave the batteries alone for a day and see what the voltage is. Too low and they are toast. Also some chargers will not attempt to charge a battery that is too low in voltage.

The last time I had a customer that was told that their batteries were bad and did not want to believe it I tested them and one read 5 volts, the other 9 volts. They were both 12 volt batteries and were 6 years old.

How old are your batteries?

 

[dhurtt]

Well, the RV was built in 2014 and the chassis in 2013. The tires were from 2013, so I have no reason not to believe the house batteries are from 2014 and the car battery from 2013 as it does not appear that anything on this was replace by the previous owner.

So, I put a charger on the house batteries – well one battery hooked to the other – positive on positive (which was cabled to another battery) and negative on negative (was not cabled to another battery) and the charger gave me a fault code that indicated the connection was bad, so do I have to disassemble the batteries in order to charge them each individually?

Still looking for my multimeter. If I do not find it tonight I am going to go into town tomorrow and buy another one. (At which point I will find my first, but that is okay as I will keep one in the RV. )

Thanks Jim.

 

[MrNoodly]

Once batteries go dead they will never take a full charge again. They will take less and less charge and last for less and less time. So, yes, you need new batteries.

The question, though, is why were they dead? Had they just sat too long before you bought the RV? Was it something wrong with the charging system? (The pulley is a clue.) Did the RV manufacturer wire something wrong so it doesn't charge properly or so there's a hidden draw on the current? Did the previous owner mess with the wiring somehow? Did you run the batteries down below 50% charge? (Do you have a monitor so you would know?) It could be any of these causes or a combination of them.

 

[Weight]

You should learn your battery cables first. Before hooking anything to them. Batteries are very dangerous to be experimenting. Do you know the specks for the battery you have? The make and size?

 

[wagoneer]

My quick and easy way to see if you have a hidden draw is disconnect the positive turn everything off off off touch the terminal with the clamp and look for a spark it may be tiny tiny but that will tell you something is drawing power.

 

[John61CT]

Only accurate test is as follows, this is the crude version.

Isolate the batteries. Charge with a known good charger at the mfg Absorb spec voltage until amps fall to very low, under 1A per 100AH new-rated capacity.

Or until amps no longer fall for over an hour.

Let sit isolated 48 hours, measure resting voltage.

Put a load device you can vary current demanded, adjust so 5A per 100AH is drawn.

Record voltage every 20-40 minutes, keep adjusting amps to that steady rate.

If your voltage drops to 10.5 in much less than 14 hours, scrap the batt, use for the core exchange fee.

Really, 16hrs is the standard scrap point, 20hrs is as-new.

Many just go until it fails, blows up whatever, but not IMO a good idea.

 

[dhurtt]

I wanted to get all of my ducks lined up before answering anyone. I appreciate all of the answers.

So now I have to confess. This really isn't so much for those in the know, but for those people that are newer to RVing and did not get a proper education that included things like the proper trades.  :s So learn from my failures!

My first concern was really "does my alternator work" or "is it 100%" because I had gotten low voltage indicators while on my last trip and now my house batteries were dead. Concerning was the statement by the Service Manager before the trip that I needed a pulley replaced. When I asked if he meant belt he said no, a pulley, and that the part would have to be ordered. But it was still okay to go on the trip.

So let's break this down.

1. I went to the RV shop again because when I asked the question "which pulley", the Service Manager did not make a note and the mechanic could not remember. So they asked me to bring it down so he could re-examine it. It turns out that the mechanic didn't actually say that there was a pulley issue. What he said was that a check engine light had come on during servicing (basically an oil change and filters), he had turned it off and told the Service Manager that "if the check engine light came on during the trip that it might be a pulley" as he was not sure if it was running smoothly. The mechanic told me that he would never do that kind of work, it was more a cautionary note. He also indicated that suggestions like that often translate into "this needs to be replaced" by the Service Manager. So that was solved. He looked at all the pulleys, said everything seems to be smooth, so disregard because I did not get the check engine light (at least not for that reason.)

2. As for the alternator, I had the vehicle running, he pulled the car battery disconnect, and it continued to run. He indicated that was a definitive test on whether the alternator was functioning or not.

3. On to the car battery and the low-voltage indicators during the trip. One of the reasons the mechanic said he would never replace a pulley on a Sprinter is because they do not have the same diagnostics tools that Mercedes does and they are not certified. They are light engine stuff and anything on the house part. But he tested the voltage on the car battery, found it strong and thus let Mercedes run the diagnostics and find the glitch in the system.

4. The house batteries are dead. So many things I did wrong, let me count the ways.

First off, either I misheard how the battery disconnect worked or the guy giving me the 10 minute tour of how things work told me wrong. Either way, I was using it incorrectly, which explains why my battery is damaged and needs to be replaced. I have a battery disconnect switch (a rocker) and it is marked "USE" and "STORE". When I was driving on the road, I flipped the switch to "USE" so my batteries were available to run the refrigerator controls, entertainment system, stairs, lights, etc. When I stopped for the night, if I was lot-docking (once in 12 days) I kept it in "USE", but if I plugged into shore power (every other night) I flipped it to "STORE" thinking that was the AC charging mode. (You know, store power...) Umm, no. Found out to my chagrin (an damaged batteries) that no, that is when you put the RV in storage. If you want to charge from AC, you are "using" them, so it stays in "USE". [blush]

What the mechanic did was we ran the engine for awhile, noting that the battery indicator on the panel showed it was charging. He put his multi-meter on and verified the house battery was charging. (By the way, the battery is a single 12V lead-acid (not AGM) unit.) He also showed me that they were not sealed so I was SUPPOSED to be watching the water level. I did not. In the end, using the alternator and a charger we got it to 13.8V (if I recall correctly), the generator could start, etc. After we turned off the engine and generator though, it was not long before the battery was exhibiting the same dead effect as before. I can no longer hold a charge.

In the end a really great education from the mechanic. He told me I should go get my own battery because Thor set it up very easily for the owner to replace it themselves. All the grounding, etc. is done, just take the hex nuts off and replace. I actually have space for two 12V in parallel if I want, or if I want to use 6V in series and parallel there is a way to lower the battery box to contain those taller batteries.

I was trying to figure this all out because the Mercedes dealer is trying to evaluate taking this in trade (for a 2017 170" WB Sprinter), so I wanted to know how bad this pulley/alternator/battery issue was. If they won't give me enough, then at least I know what I have to do to fix what issues I have.

By the way the mechanic did not charge me for anything, including his time. I learned a bit from all of you here too, so thanks for your replies and prompting me to look for things I am unaware of (and there are many such things).

I hope I can get my price. Although I do like the RV I think going through the process of either building what I need or having someone do it for me will help me understand all of the systems better and put me in a better position to troubleshoot or fix what breaks. I realize that owning a Sprinter diesel adds a lot of complexity compared to other vehicles, but honestly, I have not been able to fit in the other van cabs comfortably. Dodge Promaster and Ford Transit do not have enough leg and shoulder room compared to the Mercedes Sprinter.

If this deal falls through I think I will fix up the RV and try and sell it on RV Trader, then seriously look at a 12' step van. Older diesel, so it should not have all of the DEF complexity.

Thanks for hearing my tale of woe. If anyone gets anything out of my embarrassing lack of practical automotive and electrical knowledge then my job here is done!