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Old 05-07-2012, 04:37 PM   #11
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Originally Posted by tafische View Post
I can't see where the battery size would make a difference from the converter perspective. My guess is they recommend a size based on the battery box size. If you are willing to do some bracket mods and can take the additional tongue weight, then go for it.

Another option not as convenient - carry a spare battery in your TV if you can and hook up as needed.
That is my plan. When I upgraded to the two 6Vs, I installed a Blue Sea switch that would accommodate two banks of batteries. Right now, it's cabled only on one side the switch with the other side open but if the need arises, it'll be a 5 min trick to cable up my trolling motor battery that I keep in the bed of my truck.

See this thread for more info: https://www.jaycoowners.com/showthrea...oolbox+battery
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Old 05-10-2012, 12:54 PM   #12
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Terry,
Here is a more technical explanation;
Itís because of the source resistance of the converter vs the internal resistance of the battery.
Larger capacity batteries have lower internal resistance, and require a converter (charger) with a lower source resistance for the same performance. Larger capacity converters have that lower source resistance. Each has a range within which proper performance can be achieved, and sounds like his manual is drawing the line at group 27 size battery. Not that group 29 would not work at all, just the charging performance would be reduced to the point they donít recommend it.
Thanks David - interesting. I need to go research that a little more when I have time. I had always understood the converter to read the voltage to know when to change stages and the size of the battery really did not matter - it just took longer to charge but it sounds like there is more to it I am missing. Tell me a little bit more about what you mean on the performance reduced. Is there a point where it would damage the batteries or cause other issues?
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Old 05-10-2012, 10:42 PM   #13
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There will not be any damage when a person installs a larger capacity battery than called for, but charging will take longer. In an extreme case the battery will never achieve a full charge. For the opposite condition where the battery is undersized, the battery could be damaged by over charging (too fast or too long) and will swell and have bulging of its case. Todayís smart chargers (micro processor controlled) help to minimize this risk.

In general, the battery charger will provide 2.45 VDC per cell to be charged. The resulting current flow is dependant on the charger source resistance, the battery internal resistance and the batteryís voltage at that time. The nominal cell voltage is 2.2 volts. For sealed lead acid batteries, this current flow must not exceed 15% of the batteryís Amp-hour rating. Flooded cell types can go somewhat more than this without damage. No doubt youíve seen chargers rated as 2A, 10A, 75A etc. This is related to the internal resistance, and hence the maximum current it could deliver into a large fully discharged battery (1.8 volts per cell). Some chargers allow you to select a charge rate by switching in a bit of extra resistance to slow it down. Often they label the switch as a battery type selector. For TT converters, they size the charging circuits in-line with the above parameters.

For the OPís desire for a group 29 battery, I still think the biggest limitation is going to be physical size. The ability to achieve a full charge is a grey area. It has about 40% more Amp-hours than a group 24. Not a huge amount really. To know the fine details of his particular set-up, contacting the maker of the converter would be worth while.
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Old 05-10-2012, 10:47 PM   #14
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Very interesting answers, thanks. I ended up purchasing a group 27 battery for our needs. I just figured if the manual calls for that size (max), I will go with what they recomend. The battery will perform as needed. Thanks, I learned some by this thread, possibly more than I need to know
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Old 05-14-2012, 06:31 PM   #15
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Thanks David....interesting stuff for us tech nerds.... ;0
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Old 10-06-2017, 03:55 PM   #16
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My Jayco manual says Group 27 only also, but a group 27 won't fit in my battery box. Is a Group 24 safe? I will rarely EVER boondock.
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Old 10-06-2017, 04:32 PM   #17
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Originally Posted by KimberlyDouglas View Post
My Jayco manual says Group 27 only also, but a group 27 won't fit in my battery box. Is a Group 24 safe? I will rarely EVER boondock.
Yes, a group 24 battery is safe. It is just smaller that a group 27 in both size and capacity.
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