1996/97 CC chassis batteries do not appear to be taking a charge

[Dtjoint]

The chassis batteries have always taken a charge from the PO installed Guest two bank charger when plugged into external power. After returning from our last snow bird trip I plugged in the chassis battery charger like I always do. A few days later I noticed the chassis batteries were showing only 23vdc on the panel. I checked with a known good RMS multi meter and found the same result from + to - on the chassis battery bank. I checked all the Guest wired in fuses and all seemed good. I then tried a different battery charger that can be set for 24vdc charging. No change, the chassis batteries still show 23vdc. Sounds to me like one or more of the 12vdc batteries wired series/parallel have failed. The red light on the Guest charger stayed on all the time. With the Guest charger unplugged and the Genius brand charger plugged in the lights on it stayed on 24vdc and 25% charge light blinking.

What is the collective thinking? Should I replace the four (group 31 I think) "maintenance free" batteries of unknown age of look elsewhere?

[Gil_J]

Jerry,

It sounds like you have determined the most likely cause. You could disconnect the batteries and let them sit overnight. Then check each battery's voltage. You'l likely find that one or more batteries are reading much lower voltage than the others.

Yes, they should be group 31.

[Dtjoint]

Found four group 31 Commercial maintenance free (SLA) batteries in stock at our local NAPA for just over $500 and they delivered them to the bus. Took about an hour to label all the wires and make a record of how many wires of what size were on each post. Then I could remove all the cables with confidence that they would go back where they belong. Only issue getting the old batteries out and the new ones back in is that the battery hold down structure is welded to the chassis, then the battery tray was placed over it and the the batteries were inserted. So, to get the batteries in and out they had be be lifted and turned to get over and around that structure. Not too much of an issue for me to do ten years ago but luckily a younger neighbor came by and offered to to do that part for me. Thanks, I needed that! Once the new ones were in place and the cable ends all cleaned up it was short work to get everything back in place. The Guest external charger appears to be fine as the new batteries quickly went up to full voltage reading. Given that chassis battery bank has to supply both 24VDC and 12VDC power be sure to use a dual bank 12VDC charger and not a 24VDC unit. No year marking on the old batteries coming out but they were not changed out when the house bank was replaced in 2016 before we purchased the coach so I guess it was just an end of life issue. Glad it did not occur on the road somewhere.

[Gil_J]

Jerry,

Sign up for the free AITA membership card (https://aitaonline.com/) and get some good discounts at select NAPA stores. You would have saved over $100 on the batteries. I bought a push-pull valve the other day and the discount was nearly 50%.

FWIW, although most use dual output battery chargers on their chassis batteries, there's no need to do so. The equalizer will make sure the appropriate charge current is directed to the lower half bank of your chassis batteries. We use dual output 12V chargers primarily because it's harder to find 24V chargers that can be housed in the engine bay environment.

[Dtjoint]

Thanks for the heads up on AITA. I will check with my local NAPA today. Thanks also for the comment about battery charging the dual use 12vdc/24vdc chassis battery bank. That equalizer gizmo is new to me so I am still not sure how it works or how to know that it is working.

[Gil_J]

If the equalizer is not working you should have a Balance light or similar on the dash. If it's not working the voltage difference between the 12V and ground terminal of the equalizer will not be more than .1V lower than a reading between the 24V and 12V terminals of the equalizer. Personally, don't get alarmed if they are within .5V.

The equalizer is a fairly complex device that pulls current off the upper half bank 24/12V and sends it to the lower half bank 12/0V. This ensures two things. First, that the 12V split bank has the voltage needed for those loads. BTW, almost all loads are 12V. The second thing it does is make sure the upper and lower half banks are being charged equally.