MtnDon
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# Posted: 28 Sep 2013 12:47am - Edited by: MtnDon
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What rate is that 35 amp-hours taken at; 20 hour? The 20 hour rate is what is normally used for alternative energy systems. A rate of 100 hours is used on some batteries and that can be misleading. The other question is whether or not that battery is a deep cycle type or something else. And yet another question is whether or not this is a flooded lead-acid battery, an AGM or a Gel. Do not buy a gel cell. A battery that is not a deep cycle design will have a foreshortened life when used like this.
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One rule is to never use more than 50% of the battery rated capacity. So the 35 amp hour battery useful capacity has just become 17.5 amp-hours. You can discharge more but that will definitely shorten the battery life by a large amount.
That means with a one amp draw the battery would reach the half ways limit in 17.5 hours. One amp draw seems a little low for a CFL unless it is of very low wattage. One amp at 12 VDC is only 12 watts total.
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Is that load direct use of the DC current or through an inverter? Inverters have built in losses.
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Another battery "rule" is that leaving it in a semi to fully discharged state for an extended period of time also shortens the life of the battery. Extended is defined as more than 24 hours.
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To recharge a battery in a decent time the battery needs to have a voltage of about 14.4 volts applied to it, if it is a lead-acid or AGM battery. A trickle charger puts out less voltage than that; after all a trickle or float charger is meant to supply just a maintenance charge; lower voltage and low current. It is meant to maintain a charge not build a charge.
It could eventually recharge the battery as the battery is of rather low capacity. Might take all week. And remember the note above about decreased life when in a reduced state of charge.
Ideally you would want a charger capable of about C/10 to C/8; C= capacity. So, 35/10 = 3.5 amps to (C/8=) 4.4 amps. If this is an AGM you want to stay at no more than 3.5 amps. But you need the voltage to be higher than a float/trickle charger usually puts out.
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Myself I'd go with a larger capacity battery to cover expanded future use. Unless I was backpacking it. And it would be an AGM for safety in transporting and handling. Maybe consider LED lights instead of CFL.
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