One big or two smaller batteries?

[Ratau]

What difference does it make to use two 65 A/hour or one 130 A/hour batteries?
Is it truth to say that two batteries in parallel could work against each other? :confused:

How does the 12 / 24 volt systems work? Are the starter and alternator 24 volt and the rest 12 volt?

Danie

[britannic]

Two matched batteries will provide a longer reserve and won't get as hot/stressed during extended starts.

The weakest battery sets the condition and voltage of the system, so when replacing a dual battery system, always replace both at once.

The US M10XX series of trucks used a "heath robinson" (hokey) charging system and only the starter motor and helicopter starter outlet were 24V, the other 12V components were fed through a 12V tap from the batteries and the glow plugs were powered by 24V converted to 12-15V by a large resistor pack.

[TimK]

I concur with Britannic. Two batteries that are matched, that is same brand, model and purchased at the same time will last a long time. In a single battery with the same cranking amps, you probably have thinner plates that make up the battery and less fluid surrounding the plates then you do if you had two batteries.

There is truth behind two batteries installed without an isolator working against each other. This can be caused by the internal resistance of one battery being higher then the other. Having a matched set of batteries will help to minimize this. As a battery ages the internal resistance will tend to increase.

TimK

[Craig M]

I think weight is one issue. The single battery will be big and heavy (twice the size of a "normal" battery). Two "normal" batteries are easier to handle. Many of the older trucks (from the 50's) had either 4 "normal" sized 6 volt batteries. Or 2 large 12 volt batteries. A series/parallel switch was used for starting then running lights. If one has a location for a large 12 volt battery, and does not plan to remove it very often, I see no reason not to use it. You eliminate the extra cables (from between the batteries), and have no matching batteries issues.