Battery Charging

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Grey Fox

Joined
Apr 2, 2021
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Malibu 640
Good Afternoon.
I am wandering how accurate the battery monitor is on my Malibu 640 which is 3 months old. The panel was showing 50% this morning, I took it out for a run, for about 1 hour and it went uptown 75%, it's now back down to 50%. The inbuilt charger doesn't seem to do anything. I've had Fiat Assist out after warning light problems, he did a reset, after which he was happy that the engine charger is charging ok. I'm wandering if the weather affects the reading it's now 9 c, windy and raining in sunny Cornwall. Any advice thoughts as always gratefully received. IMG_2537.jpeg
 
An hours drive wouldn't put much in to the batteries. I've read people say those LED's for a reading are pretty poor. You'd really need to use a meter to measure at the battery/batteries themselves.
 
Both batteries
show all green lights ie 100% when on EHU
 
The inbuilt mains charger seems to be working as it should when on EHU , as suggested it may be worth getting the readings checked at the batteries with a meter to see what their actual voltage is compared to the display which it may be possible to re-calibrate

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Thanks, I’ll get a multimeter from Amazon.
 
I'd suggest the monitor is poor. My Autotrail had something similar which was pants with the pathetic lead acid battery.

For accurate voltage on battery read directly across the battery terminals. This monitor is too remote, far side of any power supply unit / fuse distribution thingy. Thin wires also affect resistance which screws the voltage prediction.

Lead acid batteries need a period of time, 30 mins to hour after charging or use for voltage to settle, as the chemical reactions in the battery end. Your 75% down to 50% may simply be that process. Even switching on a couple of lights may make it seem the voltage has dropped, yet turn them off and it could stabilise.
 
At 3 months old your motorhome will have a smart alternator. Smart alternators only charge leisure batteries properly if a B2B/Charge Booster has been fitted. This is because the engine battery is deliberately being kept at about 12.5V, which is not enough to charge the leisure battery. I would expect a new Malibu to have a B2B/Charge Booster as a standard fitting but unfortunately many motorhome constructors don’t bother. You can check whether you have a B2B/Booster by checking the battery voltages when the engine is running. The voltage to the engine battery will shoot up and down depending on the driving conditions, it goes up when you are slowing down. The voltage to the leisure battery should be a steady 14V+ until the battery is full.

Aux Battery Charging With Smart Alternators | 12 Volt Planet

A guide to the benefits of using battery to battery chargers to overcome split charging problems caused by smart alternators on modern Euro 5 & 6 vehicles.
www.12voltplanet.co.uk
 
Thank you everyone for the replies, lots of useful information.
 
Take the percentage charge scale with a large pinch of salt. Even if the voltage is perfectly accurate, the battery voltage is not an accurate indication of the percentage state of charge in most situations.

It's true that the 'resting voltage' of a battery can show the state of charge. But the 'resting voltage' of a battery means when it's not being charged, no load draining it, and having been left to settle for an hour at least. The resting voltage of a fully charged battery is about 12.7V.

If it's higher than that, something is charging it, and a very flat battery could well have a voltage of over 13V, being pushed up by the charger as it sends charging current into the battery. So the voltage while being charged is nothing like a reliable indication of the state of charge.

When it's connected to a mains hookup, the voltage gradually rises to about 14.5V, and stays there for some time, maybe a few hours. Or a few minutes if it's already very full. When the charger decides it's 100% full, it drops to about 13.5V, and stays there in 'float charge' mode, which keeps it full without overcharging.

When hookup is disconnected, it drops down to its resting voltage of about 12.7V over an hour or two.

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I would give it a right good charge, 24hr minimum and then check again after a couple of hrs off Hook up. ! Everything might be ok and its just the very small drain that will be occurring over a lengthy period.
 
Your Malibu has an 80ah Gel batter and I think it will have a 25 amp Schaudt B2B.
So if your battery was at 50 % and as autorouter says those percentage readings are very approx but if accurate you it would be down at 40 ah, you would need to put 50 ah back into the battery to get it back to 100%.
An hours driving if the B2B was outputting it's max (in practice it will be a bit less) you would only put 25 ah back into the battery.
 
I'll plug it in tomorrow and give a good charge with the inbuilt charger for 24 hours and see what happens. Interestingly the owners manual says that if the temperature is below 15c the heating should be put on as well, which I assume would gobble up a lot of the power being generated.
 
That makes more sense - I should have thought of that.

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Grey Fox said:
Thanks, I’ll get a multimeter from Amazon.
Click to expand...
You may want to consider a dc clamp multimeter which will measure the current your alternator is delivering to your batteries without breaking into the circuit, as well as voltage and other electrical tests. The following is a reliable meter at a reasonable price.

UNI-T UT210D Digital Clamp Meter AC/DC Current Voltage Resistance Capacitance Multimeter Amazon product ASIN B0753FY711
 
Thanks, I couldn’t make up my mind on which one to buy. I’ve put an order in.
 
Grey Fox said:
I'll plug it in tomorrow and give a good charge with the inbuilt charger for 24 hours and see what happens. Interestingly the owners manual says that if the temperature is below 15c the heating should be put on as well, which I assume would gobble up a lot of the power being generated.
Click to expand...
I find that an unusual statement to put into a manual ? The key thing is to ensure you have drained down correctly for the winter months if the motorhome is not being used and to ensure there is some ventilation to prevent condensation forming. Sure, if your in the motorhome, get the heating on but otherwise its just wasted energy, Your quite right to assume a lot of energy wold be used, particularly if off hook up and dependant on the top of heating used. For certain one or more fans would be required to distribute the heating around the hab area. If you establish the batteries are OK and you can easily get access to hook up, this is the way forward for the rest of the winter. If you have a half decent onboard charger you should be able to leave it switched on for very long periods without causing damage to your batteries. The details should be in its manual. Going forward if you intend to spend more time off hookup (Campsite electricity becoming expensive now) Solar panels are the way forward. Be advised, some members on here are very quick to spend your money and recommend all kind of stuff you may well not need.
 
Thanks. Just to clarify the 15c statement in the manual states " In order to guarantee the optimum battery charging the operating temperature of the living area battery must be heated to 15c via the onboard heating system.
 
Grey Fox said:
Thanks. Just to clarify the 15c statement in the manual states " In order to guarantee the optimum battery charging the operating temperature of the living area battery must be heated to 15c via the onboard heating system.
Click to expand...
Thanks for that. Most Lead Acid batteries quote their performance specification with the battery at 25 Deg C. Although they will perform at mush lower and higher temperatures. I suspect the charging difference at say 5 deg C and 25 deg C is miniscule. My hab batteries are hooked up on the driveway all winter with no issues and there is no heating on at all.

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Grey Fox said:
Thanks. Just to clarify the 15c statement in the manual states " In order to guarantee the optimum battery charging the operating temperature of the living area battery must be heated to 15c via the onboard heating system.
Click to expand...
That is just stupid I' sure someone slipped up and it should be 5°.
 
In the same section of the manual, it states "Battery charging at an operating temperature of the battery below 5c is ruled out"
 
So I guess that means the heating needs to be on below 5c which ties in with what Lenny said that the 15c is a misprint.
 
Thanks everyone I think I'm clear with a plan of action now.
 

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