battery water levels down

Since fitting the isolator, and doing a three day trip with it, I noticed that the water levels in both batteries is down by about 10mm. This seems odd to me, and I assume is an indication if the batteries being under stress. The batteries were only running the fridge overnight, between a really good charge up each day. The Redarc seems to be isolating when its meant to, and opening up the circuit very shortly after starting the car, so I think its working fine.
These are the standard 75amp hour batteries I am talking about. I know the second one needs ultimatly to be a deep cycle. I have topped up the water levels, what else can I check?

Check the alt output voltage...if its too high it will boil off the electrolyte.



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I've had to top both my batteries up once before and I have no extra hear running on them. How did u get ur redarc in? Wat did the auto electrician have to do?

Rusty, that might be part of the issue, I put it in myself. There is a sticky in this section about how people have done it, my process is in there. but it just gets wired between the batteries.

Oh ok Hehe. I'm getting mine wired in by auto electrician and maybe upper the wire size for less voltage drop. Gotta get pricing

Krankin has the right answer. There are three ways to remove battery electrolyte: punch a hole in the battery, remove it yourself, or apply too high a voltage to it and let it boil off.

If your alternator is pumping out over 14.7V it's the guy that's likely to be the culprit.

I doubt you've done anything wrong with your installation of the Redarc.

ok the voltages are; engine off, cranking 13.16 and aux 13.13V and at idle 14.19 and 14.05V
oh and I should mention there is 4G cabling between batteries running 2.4metres, as per redarc spec.

Those voltages seem good.

What were the levels before your trip/ redarc install?

Theres really only two ways that I know of for the levels to drop in three days and thats,
1/ leaking,
2/ boiling off.






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Thanks Krankin, I think it would have been a month since my last check. (sorry I should have posted that in my first post) It's not something i check too often since, they don't seem to change much. It was really just after the redarc install and workout over the weekend that I thought it worth checking. I guess I was thinking that the stock battery will have a limited life running a fridge, so I'm anticipating the need to upgrade to a deep cycle at some point. So it is possible that this drop in levels has occured over a longer period of time. I'll just monitor it more closely over the next few weeks.

I'd like to know the terminal voltage under the following conditions (2 people required):

- Drive for 30 minutes, which will be enough for the alternator to fully replenish the power used to start the engine, do NOT turn off the engine

- Measure the terminal voltages at idle

- Measure the terminal voltages at 2,000rpm

While the engine is idling, the alternator isn't really doing a lot of work.

Are there any signs of paint damage below the batteries? It would be very strange to have ALL of the cells punctured evenly though, so I'm going with a boil-off.

Generally, the fluid level of the battery should JUST touch the bottom of the riser. I'm just trying to make sure that you're actually measuring the height correctly - I don't know how experienced you are with this.

Thanks Tony, I'll give that test a go (It'll be a couple weeks though going OS in the morning). But since sunday the fluid level has not moved. so I doubt any leakage occured. Regarding the measuring, thanks for noting that, I have very limited experience in the area. I'll need to re-check my measuring.