Forum Discussion

peirek's avatar
peirek
Explorer
Jun 28, 2018

Battery Upgrade

First let me set the stage. We boondock 1-2 weeks a year. The rest of the time the trailer is plugged into shore power either in storage or at campground with hookups. We have one house GP27 wet cell battery in a rear storage compartment. The battery is in a sealed box and is vented bottom and top. The house battery is approximately 8' from charger (WFCO WF-8935AN-P) connected with 6AWG wire (I am estimating ~10' of wire). I have been taking a second deep cycle battery and connecting to front vehicle connector. This is approximately 20' from charger. I know this is not at all efficient and is mildly effective, but it has served us ok. We run the genny (Honda EU2000) for ~4 hours a day which gets the batteries back up but not fully charged.

I would like to add a second battery to the rear storage compartment but have to consider venting etc. I am leaning towards using two AGMs (6V or 12V?) so as to not worry about gassing and venting. The compartment is big enough to contain both batteries and it will still have a vent top and bottom.

I am looking for guidance on AGM batteries (6V or 12V) and brand. I have learned the Trojans are the best but are they needed for my situation (1-2 wks a year)? I suspect upgrades to the charger will be in order so would like opinions on that. I believe Progressive Dynamics is the preferred brand. I also believe the 14.8 is recommended for AGMs. Is the 6AWG sufficient for a 45A upgrade?

Thank you for your suggestions, directions, and opinions in advance.
  • peirek's avatar
    peirek
    Explorer
    Jul 01, 2018
    Thanks CA Traveler - I don't have vertical access so I would need to load the batteries and then slide into place given the base of this box is 13" tall. It would also make life really difficult to connect/fill/maintain at the height of this box.

    I was considering installing a sliding tray into the compartment but it would further reduce the height of my opening (currently @ 14.5") and probably not allow this box to work. Also would need serious anchor for the tray frame to handle the 120# cantilevered force when opened out.

    Still believe I am back to my 2 options listed above.

    A wet cell GC2 just does not seem in the cards without a custom built box - which may be doable. Fiberglass lined 1/4" plywood with .75 x.75 framing?
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jul 01, 2018
    We used this battery box which we sealed and vented for mounting inside my son’s 5er storage area.

    But we had vertical access so no weight issue.

    Hopefully you could seal a variety of boxes, JB Weld some PVC for venting and T into the existing venting.
  • peirek's avatar
    peirek
    Explorer
    Jul 01, 2018
    peirek wrote:
    @CA Traveler: Great idea about modifying a new box capable of housing the GC2s. I found these Single GC Box but cannot tell if they are capable of being sealed. I suspect not without some mods.


    I was correct. When posing the question I received several responses that said no to sealing the case.
  • BFL13's avatar
    BFL13
    Explorer II
    Jul 01, 2018
    OP, sorry for sliding this into the thread--all done now.

    Mex, thanks for the clarification. I can manage that.

    I have an 8D 250AH AGM and two 27 size 100AH AGMs banked. All three have exactly the same data sheet specs for recharging. They want 14.5-14.9 for "cycle use" and 13.8 for "float use". So a little higher voltage for "cycle use" than Lifeline and some others.

    I can do the 250 with my 55 amper and two 100s next, so they all get 20% when needed. The max of 27 per 100 is also kept by doing two 100s with the 55. All good.

    I don't need to break out the Honda 3000 at home to use higher amp chargers, which would be a nuisance.

    Thanks again for the good info!
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Jul 01, 2018
    BFL13, communications companies use chargers designed to match their bank. A gigantic bank may have 8 chargers. Or 12. And shutdown of the emergency system happens before their bank gets an over draw down. Discharges are not common. So the 20% rule may not apply. If a bank were drawn down only 30% the 20% recharge rule is far less important than it the bank was drawn to 40% or 50% remaining capacity.

    Battery chemistry just has to make itself complicated. The recharge rate is affected by the percentage of recharge achieved. Recharging slowly and constantly underachieving 100% makes life miserable for the battery.

    This is why I hammer the hell out of my AGMs when power is restored. The BORG cannot do C1 but it can do 80 amps and that's what the Lifeline is hit with. The power may go off again before even 80% is restored. But I can tell you for a fact that a whamjam recharge makes it easier to achieve .5% later on. Once capacity is lost it's either play a guessing game or do a full on capacity test.

    As a GUESS I would offer that if you discharge your AGM to no less than 70% remaining you can forget about the 20% rule altogether, but you cannot forget the .5% rule (ever). Once a week on the .5% followed the 2nd and third week by a recharge as much as is easily doable. Eqvt to your 50-90 rule, only 70-90%

    Is the 70-90 doable or is it a real pain?
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jun 30, 2018
    2 batteries in a box would be very heavy to move. Use 2 boxes with a T on the vent hoses.
  • peirek's avatar
    peirek
    Explorer
    Jun 30, 2018
    @CA Traveler: Great idea about modifying a new box capable of housing the GC2s. I found these Single GC Box but cannot tell if they are capable of being sealed. I suspect not without some mods.
    The other issue I face is access. The batteries would need to be installed into the box and the box slid through the opening and into place due to height restrictions. Still doable.

    @MEXOCOWANDERER: Duly noted that Deep Cycle Car/Marine batteries will NOT perform equivalent to a GC2. And AGM is the best way to go.

    If these darn batteries were on the tongue it would be a very simple decision.
  • BFL13's avatar
    BFL13
    Explorer II
    Jun 30, 2018
    ". It is more important to maintain a bulk charge level above 20% amp hour capacity."

    Mex, does this apply to all deep cycle AGMs or just to Lifelines and perhaps others who call for that in their spec sheets?

    My AGMs say nothing about a minimum amps recharge. They do give a max amps of "about 27a per 100AH" and a charging voltage (14.5-14.9), but no minimum amps.

    It means a lot to me, because I do the recharge- to- full of my 450AH of AGMs at home, where anything more than my 55 amp charger in the RV pops a breaker in the house the way I have things. It just takes longer to get them full at 55 amps, but at home who cares about the time it takes?

    However, if the 20% minimum does apply to all AGMs, then I have to change my routine.

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