Why to some cars have 2 batteries???

farva

I have a 97' Mitsubishi Pajero 2.8 with 2 12volt batteries and it wouldn't start yesterday afternoon, not a kick, wouldn't even turn over. I had to get a rescue truck out and he tried to start it off the mobile jump pack... not a hope. He had to use the mobile jump pack AND the Isuzu truck to jump start it, one on each battery!

I got it home and it died again, turns out that ONE of the batteries was fcuked... fair enough. So a mate of mine who is a mechanic with an 89' Pajero came over and tried to jump start it using his 1 battery on my dead one... again no luck. Turns out that because mine is a 24volt system you cant jump it using only 1 12volt battery, which rules out almost every car on the road!

Does anyone know the point of this? The only other thing that I know comes with 2 batteries is a John Deere!

Rovi

In the case of your vehicle, it has two batteries because the vehicle's electrical system is 24v; 2 x 12v batteries in series = 24v.
When one battery failed, you only had 12v left (or maybe a bit more if the other battery wasn't completely borked), so the (24v) starter motor and the rest of the system wouldn't work.

Many 12v vehicles (usually those with big diesel engines that need a lot of cranking amps) have two batteries (2 x 12v in parallel = 12v) because there isn't the space available for a really big single battery.

Del2005

The old Patrols used to be 24V also. I thought they had dropped 24V small vehicles before 98. As Rovi said they use the 2 battieries to provide the extra kick to turn over the engine, but most are now 12V as opposed to 24V.

farva

I see what you guys are saying and it makes sense. But I wonder why if it is necessary on big diesels (such as my 2.8) to use a 24 volt system, how come even bigger more modern diesels dont have to use it? Advances in technology?

This weekend I found out that I can't jump start my jeep using most cars on the road, which is really annoying if it ever happens again! In theory if I got 2 car with 12 volt batteries and 2 sets of jump leads, that should be able to jump start it, shouldn't it?

Wishbone Ash

farva wrote: »

The only other thing that I know comes with 2 batteries is a John Deere!

Many of the buses I've driven have 3 batteries.

farva

Wishbone Ash wrote: »

Many of the buses I've driven have 3 batteries.

Imagine trying to jump start one of those, that would just be a pain in the ass!!

carchaeologist

A push start would definatly be out of the question anyway:D:D

farva

carchaeologist wrote: »

A push start would definatly be out of the question anyway:D:D

Could always try and towstart it with a rope, but apparently thats illegal now!!:D

carchaeologist

Its certainly a good question!!

shanel23

My E class has two batteries - had a major problem last year where the interconnect between the two went bad and the car reported all sorts of problems - resolved by the garage after 4 hours work that the connect cable between the two had frayed - repliced the cable and all fine now

colm_mcm

Some Land Cruiser 3.0 D-4D's have 2 batteries,

not sure why, but I do know that they are quicker to start. as in you can her that the starter motor is getting plenty current!