Adding More Batteries - Converter Damage?

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Well-known member
Sep 4, 2009
Monument, CO
The vast majority of trips we take are all boondocking. The previous owner of the trailer had (3) 12v deep cycle batteries installed and we used that set up for two years.

On a recent trip, my converter died and I just replaced it with a new one. While I was fiddling with the electrical components, I removed the three existing batteries which were six years old and replaced them with a single larger battery. Now, instead of getting 36-48 hrs before having to charge, I'm getting 18-24.  I'd like to add 1 or 2 more batteries to bring up the power reserve but am worried that the additional demand on the converter may cause it die early.

Are my worries founded in reason or should I not be concerned about adding additional batteries?
First, the number of batteries makes no difference - it's the combined amp-hour capacity of the set that constitutes the "load" on the converter/charger.  Further, you would have to make a huge increase in the amp-hours to noticeably challenge the converter/charger, and even then it will self-limit its output.  You didn't mention what make/model of converter you have, but its probably rated somewhere around 55 amps/hr of capability.  With more/larger batteries, it merely takes longer to charge them up.

So what was the amp-hour (AH) capacity of the batteries you took out, and what is the AH of the new one?  Indications are the new "larger" is only moderately larger than a single one from the previous set.  A typical 3 x 12v battery bank would have about 240-250 AH of capacity (3x Group 24 batteries at about 80 AH each).  A single Group 27 would have about 105 AH and a single Group 31 would be about 130 AH.  You would need at least two of the Group 31 size to equal what you had previously. Three of the Group 27 size would yield about 300-315 AH and be a good improvement.
The new battery is a 29H and the spec sheet shows 106 AH. Since it's fairly new (and I have the space), I'd like to add two more of them.  The converter is an OEM replacement WFCO WF-9855 55 Amp converter.

My main concern was damage to the converter by asking it to run at maximum capacity for extended periods. Sounds like I should be good to go.  Thanks
In practice, a modern 3-stage converter never runs at peak  output very long.  As the batteries begin to charge, the charger load becomes less and less. The full-output bulk stage rarely lasts more than an hour or tow (depending on the battery capacity and the state of charge) and then slows down.  So yes, more amp-hours means it runs longer, but not for excessive time.

Learn about multi-stage chargers at
The only possible "Damage" to the converter is if you have fairly new batteries, enough of 'em. and they are Super hungry. you may pop the fuse. You will not. however, damage the converter.

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