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Old 11-26-2018, 03:01 PM   #1
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Question mixed Batteries and location temperatures

Three coach batteries two agm deep cycle dual purpose marine one deep cycle flooded marine dual purpose on solar charge sytem with 190 watts on a victron charge controller


One battery is in an unheated rear well one battery in a marine box behind the drivers seat third battery mounted high under the hood in a factory cradle


The charge controller is mounted in utility space with Electrical goodies and water heater close to the center battery equal distance to the others.

I know.... dont mix battery types but the flooded being a dual purpose softens this I think

My real question is which battery should go where with regards to temperature

I think I may install a precision battery isolation manager to replace the Sprinter battery isolator as I often drive for extended periods and guess I am over charging my coach batteries.

I also run a stock Paralax shore power panel but tend to boondock a lot more than plug in.

Looking for sugestions ..that dont break the bank but will optimise my setup.

Thanks for your input.
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Old 11-26-2018, 05:32 PM   #2
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I'm sorry to say that I don't think there is any easy, or cheap, solution that will make a really big difference, as temperature is probably not your worst condition. That said, I would put the wet cell in the hottest area, as wet usually handle the heat a little better.


Mixed battery types, disparate cable lengths, not great charging sources (Victron likely the best one of the three you probably have).


I think the best thing you could do would be to put them on battery switches and charge and discharge them individually.
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Old 11-26-2018, 05:44 PM   #3
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I have suboptimal batteries placement, both AGMs, one is in the engine compartment and the second one in the rear/ driver site electrical compartment. They are connected with 1/0 cables and connection to main panel/chargers/inverter is at the midpoint of these cables. Total 230Ah.

I am in the midst of installing the Magnum SBC combiner which will be working in conjunction with the factory relay. I am also installing Blue Sea OLED Amp meter which will be active during charging only. I will be able to activate the factory relay in case charging of the chassis battery will be required.

When I designed my electrical system, storage was in high priority which forced one of the batteries to the engine compartment. In case of a future replacement, I will likely have both in the back of the van.

I was contemplating using the KISAE DC-DC charger but didnít have enough room for it in the vicinity of the driver seat, so decided on ME-SBC which I bought a while back. In addition, using ME-SBC will allow me to charge chassis battery if needed, not very easy with KISAE DC charger, but, very good price - https://www.ebay.com/itm/283234585621
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Old 11-26-2018, 06:01 PM   #4
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Interesting Blue Sea ammeter, hadn't seen that one before. Shunt based at 100 amps but unusual because it can go in the positive or negative, nice feature.


I assume you could also use a 500amp/50mv shunt and multiple your readings by 5 for the larger current crowd.
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Old 11-26-2018, 06:17 PM   #5
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I have Magnum ME-ARC50 with ME-BMK/500A shunt but it is in the back of the van, not visible while driving. I will be getting this meter tomorrow and assume it comes with the shunt. My goal is to place this little Blue-Sea jewel in a place visible from the driver position. I have the Blue Sea voltage meter from the same family, great meter.
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Old 11-26-2018, 06:45 PM   #6
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Windrat - I'd keep the wet cell under the hood also. It might also be the easiest place to access for adding water when needed.

If with driving plus solar you're able to get the combined battery bank substantial charged on a regular basis - as in seeing solar on float often, then keeping them all combined as one bank might be the way to go. It would be the easiest way too.

Three batteries sharing loads should mean shallow discharges on a per battery basis. That is good.

If you find that your setup doesn't get the batteries full often then splitting the group should help. I'd keep the AGM's paired and isolate the wet cell as a first step if it comes to that.
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Old 11-26-2018, 07:23 PM   #7
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I should add that it would be a good idea to check to see if there is much voltage difference at the individual batteries when charging all together as a group. If one is lower than the others then you could make that connection and/or wiring better.
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Old 11-26-2018, 07:23 PM   #8
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A long as the AGMs match reasonably, leaving them together would not be bad. It is kind of unusual to see AGMs rated as dual purpose, but some do that. I don't know if there is a lot of difference in design, unless they are Optima style.


Some of the good/bad balance will be determined by the voltages the various sources run at, particularly the engine charging. If it is under 14v, you will get better balance in charging by a little, but also be slow, if it is at the more normal 14.4v, the AGMs will fill first and be overcharging if you try to get the wet cell full with them connected.



Having long/slow charging and discharging will be better the faster for keeping things even, but I do think that at least one selector to separate the wet from AGMs would be good, as well as trying to get the AGMs as close to same cable lengths as reasonable.


When we had mismatched wet cells in ours (2 six volt GC and ond 12v deep cycle) they worked pretty well if in the middle of the SOC range, but really got pretty bad at the upper and lower SOC areas.
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Old 11-26-2018, 07:53 PM   #9
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Probably a really good idea to get the individual OCV (resting voltages) say 24hrs after fully charging them and separating them. If the wet cell is down to 12.6V after 24 hrs rest and the AGM's are still at 12.8V or 12.9V for example then isolating or removing the battery with lost capacity should be considered.

I was assuming that all the batteries are is similar condition but if there's a real mismatch then that won't end well. The good batteries will be wasted on trying to keep the bad battery up.
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Old 11-26-2018, 08:30 PM   #10
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One possibility for the mismatch might be to have them run in the middle of the SOC range most of the time, which they may do by themselves based on use patterns anyway, and then have method to charge them to full individually (disconnect all but the one you are charging) when shore power is available or long drives happening. As long as they get to full every 5-10 charge cycles, the mid range cycling should not be overly detrimental to the batteries. It likely would be better than trying to charge all together to full, as that is where the mismatch will make a larger difference.
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