Please talk to me about AGM leisure batteries?

Discussion in 'Mech Tech' started by F_Pantos, Aug 6, 2020.

  1. Pretty sure it's OK to have a wet battery and an AGM battery charged via split charge. As long as the wet battery is sealed

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  2. mikedjames

    mikedjames Supporter

    You can always route the vent tubes outside the sleeping compartment if you have a battery that has provision for a vent tube.
     
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  3. mikedjames

    mikedjames Supporter


    The AGM is designed to gas internally and use pressure from being sealed to cause the hydrogen and oxygen to recombine.
    The wet cell battery will just gas out. If its sealed (when not designed to as in the horse box story) then it blows up at the same voltage that an AGM is just absorbing final charge. If it isnt sealed it will fizz away.

    If it is sold with the same chemistry as the AGM but in a liquid form it should be OK sold as an SLA.

    And the AGM or SLA across a wet cell battery , as a result never charges 100% and loses capacity as a result of that. Dont mix them.,
     
  4. I just paid £75 for a replacement Halfords battery. <Sigh>

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  5. If I go AGM, I'll probably change all the batteries, leisure pair first, no hassles to bypass the split charge and then recharge at home. I can replace the starter as funds permit then reinstall the split charge fuse. I don't do touring at the moment and always hookup when I get back home.
     
  6. Razzyh

    Razzyh Supporter

    I thought you needed a matching pair if on the same circuit/split charge, however if it’s not on same circuit then your ok. This has something to do with charging, but maybe that’s relevant to gel batteries, as you say @theBusmonkey can comment further.

    I will add that I did have Gel and wet battery on my bus, but the split charge couldn’t keep the gel battery topped up enough and I think it killed it. Iirc either you, @Dicky or @theBusmonkey now has/had that battery.

    I think there might be some confusion in general in this thread about gel, agm & wet batteries, or maybe I’m just confused.....
     
  7. Busmonkey has an agm leisure in his syncro.

    Gel and wet defo do not mix, I have read that agm and sealed FLA are OK to have on an alternator together but that's only what I have read.

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  8. mikedjames

    mikedjames Supporter

    It is about 0.2 volt difference in charging voltage, the SLA and AGM go a bit higher but you have to definitely stop charging them when they get hot.

    You can get battery to battery chargers that would replace the split charge system in a mixed vented / sealed setup.

    But its probably cheaper overall to find a small AGM starter battery off a stop/start modern car and then keep the simpler split charge with AGM leisure batteries.
     
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  9. Both the Bus' CTEK and my smaller one used in the workshop have an AGM mode, I also read this is to charge them to a slightly higher voltage.
     
  10. Chrisd

    Chrisd Supporter

    Ignore, if you would, my brain fart above, :oops: but do AGM batteries hold less usable charge? I've read that in a few places and so would their declared capacity be effectively less than expected therefore?
     
  11. My reading seems to indicate that AGM can replace flooded batteries on vehicles with alternators, as long as the charging system is operating correctly. The explanation on Optima's site, for example, is that can alternator is a battery maintainer and not a charger, a badly discharged battery should be recovered by a proper charger and not an alternator.
     
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  12. I was more thinking about Matt's point, a battery in the sleeping area should really be sealed.
     
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  13. theBusmonkey

    theBusmonkey Sponsor

    Well that's it really for me. In Big G the lb is under the bed.
    As Matt says I've got an AGM as a leisure and a normal wet battery as the starter. We run old alternators that aren't smart and stick in a constant maintenance voltage as you say.
    Smart alternators and smart battery to battery chargers take care of all these issues but they're expensive and are they really necessary for occasional use? I suspect not but we all like our toys;)
    So, I allow the alternator to do it's thing as per normal to the SB.
    I do have a Durite VSR which connects the 2 BUT I can isolate the lb via a simple battery isolator switch. As Mike says, AGMs can get cooked by constant unregulated charge so I just give it a belt every now and then.
    The solar charge controller is adjustable,, so I use this as my primary charger for the LB as I can adjust the parameters to suit the maintenance requirement of the AGM, which is slightly different to a FLA ie the starter battery.
    Every now and then they get a maintenance charge from a ctek. As the SB is a conventional lead acid, I do check regularly the fluid level so it's no biggie for me to plan the batteries into the maintenance schedule.
    However......Chip has same tech FLA batteries for both starter and leisure. Again, linked via Durite, maintained by the solar and tickled by the ctek (10). Leisure is 115ah. I used to have bigger but bigger amps in a case that fits our vans means lowerquality. I've had both those batteries in for 4 years. We have never, touch wood, had an issue.
    Just to add to the confusion....lol
     
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  14. theBusmonkey

    theBusmonkey Sponsor

    That's the syncro AGM battery. On maintenance top up coz the interior is stripped out. 115ah. If I could justify the cost on top of the current bodywork that's being done, and the forthcoming engine conversion, then I'd do what @pkrboo has done and go lithium.
    IMG_20200807_111545.jpg
     
  15. theBusmonkey

    theBusmonkey Sponsor

    And coz it's
    'Friday, sort the sh1t in the workshop out'
    day I thought I'd show you this for a laugh. Previous syncro lb. Weighs 35kg. What was I thinking. Now only really useful as an anchor for the boat:eek:
    Moral...don't over think it;)
    IMG_20200807_114439.jpg
     
  16. I was somewhat surprised to read that you only get about half the usable charge out if a lead acid battery, makes the literature you read sound like creative marketing.
     
  17. theBusmonkey

    theBusmonkey Sponsor

    It does and that's why it's so important to do a power audit before you even start thinking about battery technology. For example, I start with the fridge. 24hours a day running at, well who really knows coz they're buggers for creative marketing as well.
    Let's say 2amp for ours, which is a cfx dometic. Well that's already half the rated capacity and we haven't even considered propex at 1 amp for 3 hours, lighting similar, computer for films, water pump, phones etc etc.
    That's why I ended up specifying 180w of solar and to be honest id recommend 200 all day long.
    An older absorbstion fridge will kill a battery in a few hours.
    Why AGM for me on the syncro...safety and the ability to discharge and recover a bit deeper than FLA. Which ever common tech we have, there will be a discharge cycle lifetime for any given battery so any solution is always temporary.
    I will say that we live comfortably in both vans off grid by accepting we will sometimes have to run the engine if the sun doesn't play. If there's a few hours of solar input a day that usually covers the fridge use and tops up the battery for the night time cycle.
     
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  18. My current plan is to replace all three batteries with AGM, starter and both leisure batteries. Also I will fit a switch to the split charge relay so I can decide if, and when, to charge the leisure batteries. I don't want to drill the roof for solar. My only concern is both fridges run from the leisure circuit when I'm on the way to a campsite and one of them is a power hungry absorption cycle. I also intend to check what the regulator is doing (Type 4). All three batteries were on the Bus when I bought it and I suspect are even older, I need to see if they carry a date code.

    PS I run the absorption fridge on gas when not on hookup. I also intend to add one of those cigarette socket blocks with a built in volt meter.
     
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  19. theBusmonkey

    theBusmonkey Sponsor

    We u
    We have the power hungry Westy fridge as well as the Dometic. We ran this all round the State's on the leisure circuit through a tiny relay which would pop if the battery got too low. Being posh, and more grown up now, it's duty is the prosecco and beer chiller. It still makes ice amazingly.
    You'll not have an issue running off the van charging circuit into the batteries if they have that level of draw on them
     
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