Thread: Dual Battery Charging Behaviour

Try swapping the battery monitors over, or connect both to the same battery. I suspect one is giving incorrect voltage readings.

I have yet to find battery monitors that give exactly the same readings as each other.

Originally Posted by RHS58

I have yet to find battery monitors that give exactly the same readings as each other.

Mine are fairly close.

Originally Posted by winglen

Was going to ask Tim (Drivesafe) direct but thought the answer might be useful to others here.

Hi wingless and always a good move to post up this sort of question here. As you posted, it WILL help others.

As suggested, try swopping the BM2 over. They are very much the same activity just at a constantly deferent voltage.

I have 12 BM2s in use in my vehicles ( including a ride-on mower ) ad they are all within 0.04v of each other.

Also, what position is the switch on your nIn-Cab Module? Set towards the LED or away from the LED?

Originally Posted by drivesafe

I have 12 BM2s in use in my vehicles ( including a ride-on mower ) ad they are all within 0.04v of each

A sure fire way to confirm someone is a battery enthusiast… monitoring the mower :-)

Thanks for all your comments so far.

I really doubt it’s dodgy monitors, as the difference is not constant, but rather above or below consistently whether resting or charging. I’ll swap over the monitors tomorrow when I get time.

Meanwhile, I’ve kept the batteries on continuous charge for the moment, and the lag is getting closer, now within 0.07V. It looks to me like battery behaviour maybe with the Optima only coming up on a really long slow charge. See current figures below.

And Tim, my Traxide is a 2017 unit so no in cab switch. I wish I did!

Hi again Winglen, a simple test for the BM2s is to put them both on one battery for a day or two, and see how close they are.

With the way they are showing voltages now, I think you are correct in that it is most likely not the BM2s.

I suggest you try charging both batteries over night, for a few nights because, even with a problem, they should still be settling to similar voltage levels, and yours were not.

Once you have the batteries charged, get back on the thread and we can do some load testing to see if there is a problem with the isolator, or as I suspect, the cabling.

Originally Posted by drivesafe

With the way they are showing voltages now, I think you are correct in that it is most likely not the BM2s.

I suggest you try charging both batteries over night, for a few nights because, even with a problem, they should still be settling to similar voltage levels, and yours were not.

Once you have the batteries charged, get back on the thread and we can do some load testing to see if there is a problem with the isolator, or as I suspect, the cabling.

So left on charge for 2 days. And while the aux was below the main by 0.22V for half a day or so, it then jumped up and settled to within 0.06V, as predicted.

Took off the charger and left car double locked for 3 days and no keys near it. After an hour, cranking settled to 12.70V, aux above it at 12.85. After 3 days, cranking down to 12.34 (or 0.12/day), aux down to 12.57, the gap between the two increasing steadily. Isolator green light on always so batteries linked.

Given the charging readings settled so close, I think we can take the relative BM2 numbers as reliable. Just interesting behaviour that the cranking battery is higher under charge, lower at rest.

BM2 graph for the last 5 days attached.