rrliljedahl

Let me first state that I am electrically challenged.

I have installed a Benchmark Design Smart Isolator hooked up to two new deep cycle Sears Diehard Platinum P-1 Group 34 AGM Batteries in a 2010 Jeep Rubicon to power a winch and a 12 volt National Luna Weekender 52L refrigerator.

I have checked these batteries several times while day time driving for over 1600 miles this last week . I noticed that the voltage in each battery was never higher than 12.75. I was thinking that the voltage should be above 13.5 when they are fully charged.

I did no winching while on the trip.

The refrigerator was hooked up. It supposedly is a power miser as it only consumes 0.83 amp-hours over 2 hours when tested recently.

I am interested in keeping my beverages cold for as long as possible while camping over several days.

My question is why the voltage in the batteries is not higher after having been driven for that long of a time?


Ron Liljedahl

ronjenx

Here are the power draw specs for your unit:
12V -
2.5Amps average running current.
1.53 - 2.26 amp/hour average power draw.

Was the unit running when you checked the battery voltage?
If so, there is a voltage drop when a demand is placed on the battery.

Had it been recently running when you checked the battery voltage?
If so, the peak voltage after charging will drop rapidly to a point, then drop more slowly as power is consumed.

rrliljedahl

The refrigerator was running for 7 straight days.

I would check the voltage of the batteries after having driven for several hours and right after pulling off the road.

The voltage was 12.75 in both the main and the auxilliary battery. The auxilliary battery powers the refrigerator.

Thanks for the reply.

Mark Doiron

Just because you continue to charge a battery doesn't mean that it can continue to accept a charge. In fact, the theoretical maximum charge of a battery is due to the nature of the chemicals in the battery. The specific chemicals selected will determine the maximum voltage possible because of the ability of the chemicals to exchange electrons. If you need higher voltage, you either gang cells together (A cell is like a single battery such as in your flashlight. Multiple cells together, such as in a car battery, create a battery), or you select different chemicals.

Each cell in a lead-acid car battery can create 2.1 volts. You do charge it at a higher voltage, but it's not exactly the voltage that is being stored. Rather, you are causing a reverse chemical reaction that is moving electrons back so that you can recreate the original chemical reaction to generate electricity again (or to continue to generate electricity). Because a battery's fluid must boil just ever so slightly to get maximum charge, a higher voltage is applied--in the vicinity of 15.5 volts. But, that voltage level can never be stored within the battery because the chemicals are incapable of performing their electron exchange at the level.

Hope that you find that helpful.

jcs07jk

Standing voltage, no load and jeep not running, you should have about 12.5 or so. You'll see more volts if jeeps running as stated up to around 15 If you had jeep running, shut down and ran to check battery voltage, you'd see a higher voltage but it fall to about the 12.5 over a period of time.