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Old December 27th, 2011, 11:07 AM
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Justin Simmons
Join Date: Jan 2009
Location: Nashville, TN, USA
Posts: 11
Dual Battery Problem

I have a red top and yellow top dual optima system installed under my seat. It has a switch for dual batteries on, red top battery on (which I normally run), or emergency. I had the batteries checked yesterday and they tested good but low in charge and the alternator tested good as well. They are losing charge somehow though. Any thoughts?
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Old December 28th, 2011, 01:13 AM
Viton's Avatar
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Deaf Ember
Smart 4x4
Join Date: Jan 2009
Location: La
Posts: 1,231
Optima's are AGM batteries and as such, should only loose about 1% of full charge, even if you let it sit for a whole month. Without a battery isolation kit, what happens to one, will happen to the other.

On your daily drive, are you driving (or have your engine running) at least 1/2 hour? They could be chronically getting under charged by many patterns of bad behavior. Do you shut all electrical drains down before you turn off the key, head lights, park lamps, stereo, A/C, fan/blower? Do you have a high draw stereo system? Are leaving any draws on by accident, eg. dome lights, (though the '97 has the feature to shut down the dome(s), even if you leave a door open)?

My battery typically rests at about 12.4 volts after a sit overnight. I sometimes put a charger on, it set for 2 amps, overnight just to give it a little boost. I made a (+) lead on the big fuse block under the hood, so I don't have to pull the seat every time I want to give it a trickle charge. My red top lasted for 8 years. I now use a Duralast for a 1985 BMW 524td, 850 CCA.
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Old December 28th, 2011, 08:34 AM
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Nick Vogel
1997 D-90 / 2012 LR4
Join Date: May 2009
Location: Houston, Texas
Posts: 508
Does Bat 2 get isolated when the truck is off? My dual battery kit isolates the aux battery when the solenoid isnt engaged to ensure I have at least one good battery.
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Old December 28th, 2011, 08:43 AM
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1997 D90 ST #1444
Site Team
Join Date: Aug 2005
Location: Georgia
Posts: 5,329
How old are your batteries? Is one battery newer than the other? Is it wired correctly? Are all the connections tight? What is connected to each battery?

Disconnect the system and use one battery at a time, maybe one is starting to fail.

Pick up a battery tender and hook it up at night or over the weekend.

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