My father in law just got a 2000 Excursion Limited - pretty well loaded. Even got the diesel. I was looking at it and he asked me why it had dual batteries? I had no answer? What's up with that?

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1999 Expedition EB, 4x4, 5.4, LLS, K&N with airbox mod, Lund Interceptor Bug Guard, Hooker 3" Chrome tip

 

Basically, with two batteries you get an increase in current-delivering capabilities: (cold crankin amps and reserve capacity). The diesels rigs take ALOT of juice, they have to supply current to the heater grid and/or glow plugs (if equip), starter, PCM/, all the bells & whistles that came with the truck and anything else you add to it. With a single basic truck battery rated at 700 CA's & 500 CCA's might get you started in the summer, but definitely not in the winter. And with the OBDII's computers today, voltage is very crucial.

 

someone told me there is 2 batt. on my diesel, 1 for just the engine and the other for headlights, accesories, ect.

 

No-Jupiterak is coorect. Both batteries are in parallel to give increased CCA to start and run the glow plug circuits.

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1999 XLT,5.4,Wedgewood Blue,ClassIII Tow Hitches Front and Rear,K+N Air Filter,Bug Deflector,Window Vent Shades,Stainless Steel Door Edges

 

The reason it has two batteries is for start up only. At some point in time try to remove one of the batteries. The glow plugs will still work fine, but the starter will not turn. Diesels need a 24 volt starting system beacuse with the un-godley high compression that diesels run a 12 volt starter will not turn the crank. After the truck is started a battery isolator or (rather large resistor) keeps the batteries from feeding 24 volts to the entire system. The alternator only puts out 13-15 volts.

 

The Ford system uses a 12 volt starter. The batteries are in parallel, not in series at anytime. It is true some large trucks use two 12 volt batteries in series for a 24 volt starter, but this is not how Ford does it. This is a 12 volt, negative ground system in every fashion

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1999 XLT,5.4,Wedgewood Blue,ClassIII Tow Hitches Front and Rear,K+N Air Filter,Bug Deflector,Window Vent Shades,Stainless Steel Door Edges

 

Follow-up: You can usually start and run the system on one battery. The extra battery provides extra starting capacity for those cold days.

 

Granny's old '83 Oldsmo-Bubble Delta 88 diesel had 2 batteries also. This was a 5.7L (gas to diesel converted) GM 350. Without both batteries she wouldn't start in the winter. Started just fine in the summer when I borrowed one for my 72 Mustang! LOL

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F150 SuperCrew XLT

5.4L, class III towing, Oxford White, Parchment interior, Sliding rear window, Ford Duraliner bedliner, Power drivers seat, auto lights, more to come!