How can I tell if my van batteries need replacing?

bgoetting · 11-09-2009, 05:46 PM

I believe that my two van batteries need replacing. While I was camping this weekend, I let my RV battery get down to 11.6V, the starter barely turned over the engine. I hadn't used the van batteries for anything so they should have been fully charged.

After an hour of brisk driving, pulling horses up some steep hills, the voltmeter read 12.3V for the van batteries, and 12.0V for the RV battery (which is new). I'm not sure if I could expect the van batteries to be fully recharged after that drive or not.

Is there an easy way to tell if I need to replace those van batteries?

**daveb** · 11-09-2009, 10:34 PM

Get them on a shore power charge as soon as you can.

Both batteries should read higher than that after a long drive. What kind of voltmeter are you using to check them?

A new AGM house battery should be at 12.7 or slightly higher fully charged. Starting batteries, especially wet cell types should be over 13 .6 after a drive, typically in the 14v range.

Maybe you are having an alternator or a connection issue. If your separator was stuck closed both start and house systems would have been drawn down.

One way to tell If a sealed wet cell battery begins to fail, is that after a 12hr hard charge, it will start to get warm to the touch and on it's way out will be hot to the touch. A provin way to test a sealed wet cell is to use a carbon pile tester on each battery separately. Don't trust a dealer, go to a shop and have them disconnected and tested. Try the shore charge first and see if the start battery is getting hot. If you have a diesel, it's possible just one can fail and pull the other down over the night hours when the van sits.

There can also be other causes though.

LenS · 11-10-2009, 07:01 AM

If any of the batteries are wet cell, pull the vent caps and make sure that the battery water covers the plates by 1/4"(?). An hour drive might charge the starting battery but not sure about a house battery. All depends on how many amp-hours each battery holds and the amp-hour output of your alternator.

Yes, charge the batteries asap as mentioned in the first reply. Batteries should be good for 6-8 years depending on many things. For good house battery life you should try to avoid discharging the battery below the 50% charge level. That is once you are below the 12.2v level or so you are down to 50% charge level. Once you have the battery fully charged, and this can take 12-24 hours of charging let it rest for a day and measure the voltage. It should be in the 13.8v-14.5v range. Let the battery rest for a day or two with no load on it and remeasure the charged voltage. Should still be about the same level, if it has dropped significantly the battery would be suspect.

Most places that want to sell you a new battery will test your old one under load to see if it is good or not for free.

LenS · 11-10-2009, 09:35 AM

Oh yes, you can also do your own load test. I have done that and found my house battery to be good. The problem was the user (me) was being power hog.

Fully charge your house battery. Let it rest 24 hours and check the voltage. Should be 13.3v or higher.
You have to know the amp-hour rating of your house battery(s). My house battery bank is 230 ah (new battery rating...they deteriorate with age and use. So every year you get less.). So 50% of that value is my usable rating....115 amp-hours. 115 ah x 12 volts equals 1380 watts of usable power. I then turn on say 120 watts of my vans 12 volt lighting. Leave it on for 11.5 hours ( 1380watts/120watts per hour equals 11.5 hours of use). Then again let the house battery bank rest for 24 hours and take a battery voltage reading. The value should be about 12.1 to 12.3 volts. If it is house batteries are supplying all the power they were designed for.

Rule of thumb: To get the most out of your batteries you should only charge and discharge them at a rate no higher then 10% of their amp-hour rating. My case again that would be 23 ah per hour drain or "fill" rate.

jeff@work · 11-10-2009, 11:02 AM

do you know what type of isolator/separator you have on your van?
I just have the factory ford one and the way it works is with the ignition in the off position the batteries are separated, with the ignition in the on position they're joined together... if i had drained my house batteries down to 11.6 there's a pretty good chance I would have trouble starting my van as well since the house batteries would be pulling on the starting battery at the same time i'm trying to start the van.

The voltages Len quoted seem a bit off to me, 13.3 is about what i would expect my batteries to be taking as a float charge. A fully charged battery should be around 12.7-12.9 V depending on the temperature.

Depending on how many amp hours your house battery is it could take quite a bit of driving around to fully charge it, i have 330 amp hours and driving around for an hour really doesn't do a whole lot for recharging it, especially one that had been drained down so low. Also letting your battery get down to 11.6 will really reduce the lifetime of that battery, ideally you shouldn't let it go below 12.1 - 12.2V.

The voltages you're quoting sound normal to me, I would definitely recharge the house batteries and then see if you have any other problems with starting the van.

Here's some great info on batteries http://www.solar-electric.com/deep_cycl ... ry_faq.htm If you scroll down to "state of charge" about 3/4 of the way down you'll see a chart showing voltages and state of charge.

bgoetting · 11-13-2009, 08:25 PM

Thanks for the help!

I charged all batteries on shore power for 24 hrs. My new AGM 4D is reading 12.6V but drops to 12.3 when I turn on the frig and inverter. Doing this did not effect the volt reading of the starter batteries so I believe that the separator is working properly (its the new automatic separator without the switch on the dashboard).

The starter batteries were at 12.7V but dropped to 11.6V quickly when I turned on the headlights and Hella lights then dropped to 11.0V when I turned on the ignition and the vent fan. The vehicle started OK so I'm guessing that the separator links the batteries when I engage the starter, or maybe these voltages are normal and the batteries are fine. I couldn't feel if the starter batteries were warm after charging because they are in their metal cases and I don't know how to open them.

To confuse matters, I plugged my tester into my Honda which is having no battery issues. It read 12.5V then dropped to 11.5V when I turned on the lights and fan (engine not running).

My voltmeter is similar to the one SMB provides. I got it at an auto parts store. It agrees with the voltmeter built into the inverter.

Can anyone help me interpret this?
Those batteries don't look easy to get to. Can any repair shop replace those? Expensive?

BG

jeff@work · 11-13-2009, 08:55 PM

That's an easy one. The only way to get a correct voltage reading on a battery is when there is nothing drawing power from it. The measured voltage will always drop when you turn things on such as the headlights, fridge, etc. So basically the voltages on your batteries sound just fine.

bgoetting · 11-14-2009, 08:37 AM

If my house battery is low, can it really draw power from my starter batteries when I turn on the ignition, causing my vehicle to not start? I thought the separator only linked the circuits if the house battery has more voltage than the starter batteries?

My friend's SMB has the dashboard switch to link the circuits. That seems like a much better idea than this automatic separator. I have no idea how my starter batteries are doing unless I crawl under and disconnect the house battery.

**BroncoHauler** · 11-14-2009, 09:56 AM

#26 on my list of things I want to change/add to my SMB but probably never will:

BlueSea - ML-Series Heavy Duty Automatic Charging Relay
* 500 Ampere continuous rating
* Magnetic Latch (ML)-ACR draws very low current (<10 mA to monitor terminal voltage) in the "ON" or "OFF" states, and draws moderate current for very short time when changing state
* Start Isolation (SI)-Can be configured for temporary isolation of House loads from Engine circuit during engine cranking to protect sensitive electronics
* Engine Isolation (EI)-Can be configured for isolation of two engines while both are running to protect engine electronics and maximize alternator output
* Senses charging on two battery banks
* Supports high-output alternators up to 500 Amps
* LED output to remotely indicate when batteries are combined, isolated, in voltage lockout, in Start or Engine isolation

http://bluesea.com/category/2/productline/388

Herb

jeff@work · 11-14-2009, 10:14 AM

Your description might very well be how your separator works... it certainly is how it should work! Someone else will need to chime in to answer that question as i'm not sure what separators Sportsmobile uses... you might even want to contact Sportsmobile to see what they say. My van came setup with the ford factory separator and unfortunately mine is not smart enough to work that way.
I suppose one way you could double check would be to drain the house batteries down lower than the starting battery, verify the voltage on the starting battery, turn the ignition to the on position (without starting the van) and see if the voltage at the starting battery drops.