energy bank for brunnhilde - part 1

I have not post for months and have a lot of catch up posts to write. I have hundreds of photos that I want blog posts to document them, for posterity.

The coach batteries in Brunnhilde has been losing capacities steadily noticeably since a couple of years ago. Recently they have gotten to the point of threatening the ability to support the DC refrigerator during an overnight stop transiting interstate highways in a trip to Iowa to pick up the open car trailer. It happen after I used the audio system quite loud for hours and then went to sleep. I estimate that must used up extra 25 Ah of energy. When I woke up I noticed the voltage had drop below 12.0 V.


As the existing batteries are Optima Blue Tops they size cannot be used to find replacements. I researched the equivalent battery group and realize they are Group 31. Like most owner I first researched the AGM offerrings. They starts from $300 and some are close to $500 each. I nearly bought a set of Napa house brand falling for their waste of time 20% off sales which turns out will not apply to these battery due to the gimmicky technicalities which I would not get into.

I decided to explore my other idea - that is to find a good quality wet cell deep cycle in the group 31 size. I did not like the prices of them and the limited offerings. I then turned to my other idea - to find the closest size RV/Marine battery from Costsco limited offering of batteries. Costco does not have group 31 of any kind.

to test one more time that the coach batteries indeed has very little residue capacity I left these two 10W halogen fixtures on overnight

by morning the battery voltage had dipped to 10.3V

I drove to Costco and picked these up - for $79 each

these are the Optima Blue Top AGMs

I used this clamp meter to determine which path the current from the in vehicle charger comes in

the Costco group 27 is slightly smaller than group 31 but the price is very hard to beat

I knew there is this vent hole in the battery compartment making the used of wet cell deep cycle batteries safe

nice and clean after some soup and water; note that the battery tub that is an integral part of the potable water tank are the revised version with strengthen features to support the massive weight of two group 31 batteries

the next potential fitment challenge is would the center hold-down bar fit against these batteries and it just barely if one center the slightly smaller batteries in the battery box (I used a couple pieces of plywood as spacers on two ends to take up the gap left behind by the slightly shorter batteries

someone added this self-resetting breaker that is for the in-vehicle charger

this ratchet wrench made reinstalling the cover bolts easier

this is the charge voltage of the in-vehicle charge at full charge

Now the proof of the pudding is how well they fair during dry camping. I view the selection of these batteries representing the lowest cost per charge cycle, much cheaper than buying a set of premium group 31 AGM. There is no way I would consider a pair of gel cell which are even more costly than premium AGM.