Can someone explain battery discharge

[flarider]

I think I have at least one bad batter in my bank. I can only go about 1.5-2 hours before I hit my LBCO which is set at 11.7, I did have it lower and it was about the same It looks like I am drawing about 18 amp (240 watts) with just the basic on, refrigerator, DirecTV receiver and pepwave router and 28 amps when the refrigerator compressor kick on.

When the batteries got below 11 volts I checked them to see if I could find a bad battery but got some odd reading. Look at picture below, all 8 batteries had 10.7 volts each 12 volt bank had ~10.7 volts and ever other battery was ethier ~6.3volts or ~4.3volts. Why would they discharge that way? Is this normal?

 

[Joe Hogan]

Here is a reasonably good guide. A cheap hydrometer is very useful with flooded acid batteries.

Please visit wikiHow directly

 

[Neal]

What type of batteries are they?

 

[flarider]

They are Harris AGM batteries. In a 2018 DSDP

 

[flarider]

Here is a reasonably good guide. A cheap hydrometer is very useful with flooded acid batteries.

Please visit wikiHow directly

I should have said, They are AGM batteries.

 

[Neal]

I know @Chuggs is a busy man right now, I’ll shine my special light up in the sky and see if he can chime in when available.

 

[Old-RV'er]

Assume you have no corrosion on any of the terminals, and all are tight. Although long shot, make sure all circuits into the 120V Breaker panel are also tight. I found some well not lose, but not as tight as they should be. The batteries are young enough, there should not be any bad ones, but life is not perfect. I don't think you can check the complete bank and isolate the bad one, they most likely will have to be tested individually. I think I would contact place of purchase/vendor and see if they have a field tech who can do that for you. My reasoning is that if battery is bad and you find it, they are going to test it again anyway, and then go through the depreciation process to determine what it's worth in replacement dollars. If you do the testing, wear good rubber gloves, and make sure you disconnect the positive cables first because of the inverter unit. Twas me, I would take it someplace knowledgeable and then make sure they disconnect positive cable first, otherwise new inverter will be needed.

 

[Buly]

Most likely you have one bad battery. Only way to find it is to disconnect all from each other, and load test them one by one.
it happened to me. I installed 6 new Trojans in my golf cart. But they did not last more than half our before low voltage light came on. Turned out one of them was draining down the whole bank.

 

[Chuggs]

Buly is right. Best way to check is to disconnect them…rest…test separately.

If you are plugged into shore power…and have a magnum inverter…you can leave the coach in pass thru mode. Your fridge will stay on… but the only lighting inside that works are the two lights over the cockpit seats (chassis battery), and the microwave under hood light. So, it may get dark inside.

At ME-RC turn Charger OFF…turn Inverter OFF…turn salesman switch relay OFF. Check fridge…see if you are still in pass thru mode. It needs to be established prior to disconnecting stuff…it won’t re-establish if lost, until the 12v system is ON again.

Disconnect the positive lead from the inverter and wrap securely to prevent accidental grounding. This is easily accomplished at the 350A catastrophic fuse. This prevents damage to ME-AGS and ME-BMK, if installed.

Disconnect all the negative leads to batteries.

Disconnect remaining positive leads…use care when disconnecting the lead going to bi-directional isolator…either when working on the house or chassis. If for some freak reason the relay is closed...that line will have power from the opposite bank. Just wrap it carefully to prevent accidental grounding.

Disconnect parallel and series connections.

Rest the batteries to dissipate any surface charge.

Take reading of individual 6v batteries.

Clean all terminals and contact points…and reassemble bank in the exact reverse order.

Honestly…I really can’t explain the readings you got. If only one pair had those readings…I might think there is bad wiring inside a battery to it’s terminal. But each pair read low on one battery…alternating like that. I do believe it’s better to completely separate them for this level of troubleshooting.

After you‘re done…don’t forget to check your charger and inverter are both back on. Salesman switch repowering coach. Everything back to working.

Normally…batteries are installed at the same level of health and charge. They should charge evenly, unless there are contacts making a poor connection. Newmar has two different wiring schemes…One like yours for AGM, and a strange way of pairing batteries for Flooded Lead acid, (protrusions on cases prevent using copper series jumpers if aligned like the AGMs) Ideally…any pathway thru any given pair…should be equal…although I don’t think the imbalance caused by different pathway lengths is all that significant. Newmar doesn’t concern themselves with it.

If you find a bad battery..you could try charging on a 6v charger to see if it is really bad (dead cell) or just somehow didn’t get it’s fair share of the charge…due to bad connections.

 

[flarider]

I have a load tester on order. Will test each battery and see what it shows, but already planning on getting 8 new LifeLine batteries. Not being an expert on batteries I did know if it was normal for them to discharge that way and if I let it go longer the 4 batteries that had the 6 volts would have drawn down to 4 volts to balance the batteries that where already at 4 volts.