Difference between revisions of "Bigger battery"

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Latest revision as of 08:22, 9 July 2018

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File:IMG 0774.JPG
This is a group 31 Marine battery, 13 inches long, 75 pounds

This page is about getting more battery in your vehicle so you can:
Have more reliable cold starting.
Use an Alternator disable switch
Do an Alternator delete
Do more Engine Off coasting (EOC)
Run a large power inverter with the engine on.
Run a small power inverter or small load with then engine off.

All with out killing your starting battery.
Remember, your vehicles original equipment starting battery was never intended for any of this.

How batteries are rated for total power capacity

Amp Hours (Amps x hours), the total electrical charge the battery can deliver. The Amp Hour rating comes from the amp load that the battery can sustain for 10 or 20 hours at a temperature of 78'F before dropping to 10.5V.
Reserve Capacity (RC or RCM), the number of minutes a battery can sustain a 25 amp load at 80'F before it drops to 10.5V.
Reserve Capacity for deep cycle traction batteries can also be measured as number of minutes holding a 75 amp load before dropping to 10.5V
Peukert's Law, the scientific law explaining why you get less amp hours the faster you discharge a battery.

How batteries are rated for engine starting

CA or Cranking Amps, The amount of current a 12 volt battery can produce for 30 seconds with out dropping below 7.2V at 32'F.
CCA or Cold Cranking Amps, The amount of current a 12 volt battery can produce for 30 seconds with out dropping below 7.2V a 0'F.
When you install a bigger battery you get more of these, don't worry about having too many Cranking amps, you can never have too many. If doing a drop in upgrade make sure the deep cycle battery has enough cranking amps to start your vehicle during the winter as deep cycle batteries tend to have low lower cranking amps for their size compared to a dedicated starting battery of the same size.

(Temperatures are in Fahrenheit as to not confuse degrees Celsius and Charge rate as both are represented by a number followed by the letter "C")

Battery selection

Traditional flooded deep cycle lead acid batteries take a very long time to reach full charge. Up to 8 to 12 hours just to reach 80% charge.
A valve regulated AGM or gel cell deep cycle marine battery on the other hand is perfectly designed for alt delete and EOC. In its normal life a deep cycle marine battery does double duty provides starting power for the main engine and powers lot of little stuff when the main is off line. These batteries are used to run pumps, lights, trolling motor, fans and more. The Valve Regulated Lead Acid battery (your deep cycle AGM and gel batteries) have slightly different plate chemistry from a traditional flooded deep cycle battery allowing them to almost fully recharge in 2 to 3 hours. But VRLA batteries are more vulnerable to thermal run-away during heavy charging. Follow all manufacturer instructions to the letter when trying to "fast charge them". When charging batteries slow and steady wins the race.
The battery pictured is an Absorbed Glass Mat deep cycle Marine battery.
I have seen this run away failure may times over the years, always the battery gets really hot due to internally shorting out, some times part of the battery can melt and give off a really bad sulfuric acid and burnt plastic smell. I have yet to see an AGM battery fail in truly spectacular catastrophic manor where they catch fire or explode. It could happen.

Instructions for mod

There are 3 ways to preform this mod:
Simple Upgrade.
This is where you stick with the same size or sizes recommended by your original equipment manufacture and you are just installing a gel or AGM version of your standard flooded lead acid battery.

  -This is just a simple upgrade
  -You know it will always work
  -Only useful for short EOC and turning your engine off at stop lights

Stuff the largest battery that you can make fit into the existing battery compartment:

  -Not as simple
  -Requres research of battery sizes and some trial and error
  -Auto parts store clerks should assist you
  -Good compromise for the EOCer
  -Battery hold down may need to be modified
  -If you are brave, alter, modify or fabricate a new battery perch making it wider, deeper, longer or taller as needed

Full battery relocation:

  -Safety concerns
-Requires fabricating a way to secure the battery -Requires fabrication of new wiring -No longer constrained by vehicle battery compartment -You can use multiple batteries -Much more expensive -Battery may be used as ballast improving weight distribution -This is what you have to do if you want to run an alternator delete for extended trips -Highly recommended when using Lithium batteries

If you put a bigger battery in the existing compartment just reuse the existing battery cables if possible. Some times you may need to make them longer or put different lug ends on them if switching connector styles. If you relocate the battery you should go at least one size larger than the factory battery cable. Use welding cable if you want highly flexible cable that does not have to make real tight turns. If you would rather use cable that retains a shape when you bend it and that can handle tight turns then you want multi stranded THHN, THWN rated power cable.
Factory battery cables tend to be kind of in the middle of welding cable and multi stranded TH cable, its not as flexible as welding cable but will tend to hold its shape kind of like TH cable, but remains much more flexible than TH cable.

User experiences

Please enter your user name and any relevant data in the table<br>

User data
User Name Car Make, Model, Year Cost of Mod Time to Perform Mod MPG Before Mod MPG After Mod MPG improvement guess Instruction Link
Example Data Saand Example Data Mazda, 626, 1991 Example Data $5 USD Example Data 1 Hour Example Data 27.2 Example Data 29.8 User mod detail or measurement detailed data

Problems / Consequences of mod

After a long EOC the alternator belt will likely squeal when you fire the engine back up (unless you have done an alternator delete).
Vehicle weight will be increased by going to a larger lead acid battery.
If the battery is relocated and increased in size it may change handling charaistics.
Vehicle handling and weight distribution can be hindered or improved depending on how the mod is executed.
Don't put the battery between the fuel tank and bumper.
If you alter the vehicle wiring or battery position don't allow battery cables or the battery its self to rub on live machine elements such as axles, control arms, brake lines, the ground, springs or belts/pulleys.
If you replace a starting battery with a deep cycle battery of the same size you can end up with less cranking amps.


Forum thread links

Bigger battery

External links to battery suppliers


Related mods and considerations