Battery hygiene

Airstream batteries on charge

I wish this was a post about installing Lithium batteries and a $12,000 solar setup. Sadly what follows are rather more mundane observations about battery maintenance.

Our Airstream shipped with two fairly inexpensive Interstate SRM-24 deep cycle batteries. These retail for about $120 each. I have great respect for them – they kept us going for over two days in a blizzard.

Unfortunately the lifespan for deep cycle batteries in RV applications seems to be about two years and they don’t age gracefully. This is a function of two things:

  1. The standard factory installed charging systems are poor and never fully charge the batteries, which leads to death by sulphation. One of the best resources I have found on this topic is HandyBob’s blog.

    The remedy is to install a three-stage charging system. Outback chargers are highly regarded but costly at $1,700.

  2. Boondockers in particular tend to discharge batteries more than they should. Guidance on discharge cycles and effect on lifespan can be found directly from the battery manufacturer. For the SRM-24s, find a helpful document here . A rule of thumb is not to discharge batteries more than 50%.

    To monitor charge state properly you’ll need a real battery monitor. The factory installed one that also measures the holding tank status is insufficient. The Bogart Engineering Trimetric TM-2030RV-F is a good one – I bought it myself.

If you aren’t into boondocking it’s not unreasonable to simply regard batteries as disposable. After all, for the $1,700 cost of an Outback charger you could buy 7 sets of SRM-24s. If you get two years out of each set, that’s 14 years worth of batteries.

But if you are into boondocking, battery life is material. And the thing is, batteries don’t get to two years and then die. They die slowly, reducing the time you can run without shore power. So at some point you’ll find yourself running your generator 20 hours a day.

If we found ourselves living on the road again (you never know), then I’d probably invest in a 3-stage charger/inverter.

What about weekender boondocking? That’s the sort of boondocking we’re doing these days. Our goal is to be off the grid for two or three nights and run the generator infrequently. Even quiet generators are loud.

Our batteries were new in December, 2012. I know that because it’s printed on a label on the top of the battery. At nearly three years old they are still working well. We haven’t made any modifications to the factory power setup.

Airstream batteries

This is what I do.

  1. At the end of a trip remove the batteries and take them home. Tip: before yanking them out, take a picture so you can wire them back up! I have some clear plastic contractor glasses I wear when messing with batteries. 10 minute task.

  2. Ensure the electrolyte levels are correct. Pop open the two caps and peek into the individual cells. Top off with distilled water if necessary. Wear eye protection! 2 minute task.

  3. Leave them on charge in the garage using a BatteryMINDer 3-stage charger. $140. It is conceivable you could get a build up of explosive gas storing and charging in a small enclosed space.  Our garage is big and the door is opened quite often. I probably wouldn’t do this in a closet in the basement.

    The very first time I used the BatteryMINDer I de-sulphated the batteries one at a time over a period of several days. Simply follow the directions. I then connected the batteries together in parallel and now use this device to re-charge/maintain the charge when the Airstream is in storage.

  4. When we head off for a trip, I take the batteries back and re-install them. 10 minute task.

On September 14th, after taking the batteries off charge and letting them sit for 12 hours, I then tested them using a Schumacher Electric BTF-250. Results below.

MCA: 690
CCA: 550

Test Results

Battery A
702 MCA
586 SAE (CCA)

Battery B
696 MCA
562 SAE (CCA)

The local Interstate Battery dealer will also perform a load test. If I get around to that I’ll post the results.

Anthony, Waukee, Iowa

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