Aux Battery re-charge issue

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Paul Rosser about 5 months ago	I did a test with the Waeco the other day. Ran it to see how long it could safely run for and to ensure the second battery was used. Running a Redarc SBI dual battery isolator. Old model I believe. Ran it for just over 24 hours and was still going. Aux (New Deep Cycle) battery was well into the 11 volt range. Primary (Year old 4wd batt) was still at 12.5. All good. The reason for the test is to see. 1: How long I can run the waeco for : PASS > 24 hours. Batt still at 11.5 ish volts 2: Test Redarc to ensure the truck would still start after running the waeco for an extended period and only aux batt was discharged : PASS 3: Ensure charging was okay afterwards: FAIL I ran it low to ensure if it happened in the bush then I would not be stuck. In the Pajero cabin I have two feeds, one dedicated from each battery with a single voltmeter and a switch to monitor each. After 24 hours. Pri = 12.5v, Aux 11.5 volts (Approx) Start engine. Pri = 14 volts, Aux 11.5 volts Drive for 30 minutes. Pri = 14v, Aux 11.5 volts Turn off motor. Pri = 13v, Aux 11.5 volts After 30 secs (approx). Pri 12.5ishV. Aux suddenly jumps to 12.5ishV. Same issue the next day. Sounds like for some reason that the redarc is isolating the battery because of the big voltage drop. Do I need to flick the override switch to get both batteries charged? Previously both batteries have sat at the same voltage.
Dylan @ REDARC permalink	Hi Paul, Thanks for your post. From the fault description you have given, it sounds like the isolator has voltage drop across its contacts and may be faulty. The giveaway is when you mentioned that the start battery side is 14 volts, which would mean the isolator is on, and the auxiliary side is still 11.5 volts. If the isolator is on and there is a difference between the two voltages, it means that there is no connection between the two batteries. All Redarc products feature a 2 year warranty, i recommend sending the unit back for us to check out.
Paul Rosser permalink	Are there more test I can do? Would be a pain ripping it out and not having it for a week or so. It def seems to be working every other way and once the voltage difference between the two batteries got close enough it then started to charge fine.
Dylan @ REDARC permalink	Paul, It sounds intermittently faulty, and in the future will only get worse if that is the case. I am still going to recommend sending the unit back.